diff --git a/bson/__init__.py b/bson/__init__.py
index 4a511f53c..b4e6aecdc 100644
--- a/bson/__init__.py
+++ b/bson/__init__.py
@@ -202,7 +202,10 @@ def _get_object(data, view, position, obj_end, opts, dummy):
     obj = _elements_to_dict(data, view, position + 4, end, opts)
 
     position += obj_size
-    if "$ref" in obj:
+    # If DBRef validation fails, return a normal doc.
+    if (isinstance(obj.get('$ref'), str) and
+            "$id" in obj and
+            isinstance(obj.get('$db'), (str, type(None)))):
         return (DBRef(obj.pop("$ref"), obj.pop("$id", None),
                       obj.pop("$db", None), obj), position)
     return obj, position
diff --git a/bson/_cbsonmodule.c b/bson/_cbsonmodule.c
index 2eb9e992d..67ee01c72 100644
--- a/bson/_cbsonmodule.c
+++ b/bson/_cbsonmodule.c
@@ -1506,6 +1506,71 @@ static PyObject* _cbson_dict_to_bson(PyObject* self, PyObject* args) {
     return result;
 }
 
+/*
+ * Hook for optional decoding BSON documents to DBRef.
+ */
+static PyObject *_dbref_hook(PyObject* self, PyObject* value) {
+    struct module_state *state = GETSTATE(self);
+    PyObject* dbref = NULL;
+    PyObject* dbref_type = NULL;
+    PyObject* ref = NULL;
+    PyObject* id = NULL;
+    PyObject* database = NULL;
+    PyObject* ret = NULL;
+    int db_present = 0;
+
+    /* Decoding for DBRefs */
+    if (PyMapping_HasKeyString(value, "$ref") && PyMapping_HasKeyString(value, "$id")) { /* DBRef */
+        ref = PyMapping_GetItemString(value, "$ref");
+        /* PyMapping_GetItemString returns NULL to indicate error. */
+        if (!ref) {
+            goto invalid;
+        }
+        id = PyMapping_GetItemString(value, "$id");
+        /* PyMapping_GetItemString returns NULL to indicate error. */
+        if (!id) {
+            goto invalid;
+        }
+
+        if (PyMapping_HasKeyString(value, "$db")) {
+            database = PyMapping_GetItemString(value, "$db");
+            if (!database) {
+                goto invalid;
+            }
+            db_present = 1;
+        } else {
+            database = Py_None;
+            Py_INCREF(database);
+        }
+
+        // check types
+        if (!(PyUnicode_Check(ref) && (database == Py_None || PyUnicode_Check(database)))) {
+            ret = value;
+            goto invalid;
+        }
+
+        PyMapping_DelItemString(value, "$ref");
+        PyMapping_DelItemString(value, "$id");
+        if (db_present) {
+            PyMapping_DelItemString(value, "$db");
+        }
+
+        if ((dbref_type = _get_object(state->DBRef, "bson.dbref", "DBRef"))) {
+            dbref = PyObject_CallFunctionObjArgs(dbref_type, ref, id, database, value, NULL);
+            Py_DECREF(value);
+            ret = dbref;
+        }
+    } else {
+        ret = value;
+    }
+invalid:
+    Py_XDECREF(dbref_type);
+    Py_XDECREF(ref);
+    Py_XDECREF(id);
+    Py_XDECREF(database);
+    return ret;
+}
+
 static PyObject* get_value(PyObject* self, PyObject* name, const char* buffer,
                            unsigned* position, unsigned char type,
                            unsigned max, const codec_options_t* options) {
@@ -1552,7 +1617,6 @@ static PyObject* get_value(PyObject* self, PyObject* name, const char* buffer,
         }
     case 3:
         {
-            PyObject* collection;
             uint32_t size;
 
             if (max < 4) {
@@ -1585,55 +1649,10 @@ static PyObject* get_value(PyObject* self, PyObject* name, const char* buffer,
                 goto invalid;
             }
 
-            /* Decoding for DBRefs */
-            if (PyMapping_HasKeyString(value, "$ref")) { /* DBRef */
-                PyObject* dbref = NULL;
-                PyObject* dbref_type;
-                PyObject* id;
-                PyObject* database;
-
-                collection = PyMapping_GetItemString(value, "$ref");
-                /* PyMapping_GetItemString returns NULL to indicate error. */
-                if (!collection) {
-                    goto invalid;
-                }
-                PyMapping_DelItemString(value, "$ref");
-
-                if (PyMapping_HasKeyString(value, "$id")) {
-                    id = PyMapping_GetItemString(value, "$id");
-                    if (!id) {
-                        Py_DECREF(collection);
-                        goto invalid;
-                    }
-                    PyMapping_DelItemString(value, "$id");
-                } else {
-                    id = Py_None;
-                    Py_INCREF(id);
-                }
-
-                if (PyMapping_HasKeyString(value, "$db")) {
-                    database = PyMapping_GetItemString(value, "$db");
-                    if (!database) {
-                        Py_DECREF(collection);
-                        Py_DECREF(id);
-                        goto invalid;
-                    }
-                    PyMapping_DelItemString(value, "$db");
-                } else {
-                    database = Py_None;
-                    Py_INCREF(database);
-                }
-
-                if ((dbref_type = _get_object(state->DBRef, "bson.dbref", "DBRef"))) {
-                    dbref = PyObject_CallFunctionObjArgs(dbref_type, collection, id, database, value, NULL);
-                    Py_DECREF(dbref_type);
-                }
-                Py_DECREF(value);
-                value = dbref;
-
-                Py_DECREF(id);
-                Py_DECREF(collection);
-                Py_DECREF(database);
+            /* Hook for DBRefs */
+            value = _dbref_hook(self, value);
+            if (!value) {
+                goto invalid;
             }
 
             *position += size;
diff --git a/bson/json_util.py b/bson/json_util.py
index 5498bf044..fe0bfe069 100644
--- a/bson/json_util.py
+++ b/bson/json_util.py
@@ -121,9 +121,6 @@ _RE_OPT_TABLE = {
     "x": re.X,
 }
 
-# Dollar-prefixed keys which may appear in DBRefs.
-_DBREF_KEYS = frozenset(['$id', '$ref', '$db'])
-
 
 class DatetimeRepresentation:
     LEGACY = 0
@@ -463,7 +460,9 @@ def object_pairs_hook(pairs, json_options=DEFAULT_JSON_OPTIONS):
 def object_hook(dct, json_options=DEFAULT_JSON_OPTIONS):
     if "$oid" in dct:
         return _parse_canonical_oid(dct)
-    if "$ref" in dct:
+    if (isinstance(dct.get('$ref'), str) and
+            "$id" in dct and
+            isinstance(dct.get('$db'), (str, type(None)))):
         return _parse_canonical_dbref(dct)
     if "$date" in dct:
         return _parse_canonical_datetime(dct, json_options)
@@ -675,10 +674,6 @@ def _parse_canonical_regex(doc):
 
 def _parse_canonical_dbref(doc):
     """Decode a JSON DBRef to bson.dbref.DBRef."""
-    for key in doc:
-        if key.startswith('$') and key not in _DBREF_KEYS:
-            # Other keys start with $, so dct cannot be parsed as a DBRef.
-            return doc
     return DBRef(doc.pop('$ref'), doc.pop('$id'),
                  database=doc.pop('$db', None), **doc)
 
diff --git a/doc/changelog.rst b/doc/changelog.rst
index 828d8b038..d7a68436e 100644
--- a/doc/changelog.rst
+++ b/doc/changelog.rst
@@ -104,6 +104,14 @@ Breaking Changes in 4.0
 - Changed the default JSON encoding representation from legacy to relaxed.
   The json_mode parameter for :const:`bson.json_util.dumps` now defaults to
   :const:`~bson.json_util.RELAXED_JSON_OPTIONS`.
+- Changed the BSON and JSON decoding behavior of :class:`~bson.dbref.DBRef`
+  to match the behavior outlined in the `DBRef specification`_ version 1.0.
+  Specifically, PyMongo now only decodes a subdocument into a
+  :class:`~bson.dbref.DBRef` if and only if, it contains both ``$ref`` and
+  ``$id`` fields and the ``$ref``, ``$id``, and ``$db`` fields are of the
+  correct type. Otherwise the document is returned as normal. Previously, any
+  subdocument containing a ``$ref`` field would be decoded as a
+  :class:`~bson.dbref.DBRef`.
 - The "tls" install extra is no longer necessary or supported and will be
   ignored by pip.
 - The ``hint`` option is now required when using ``min`` or ``max`` queries
@@ -123,6 +131,7 @@ See the `PyMongo 4.0 release notes in JIRA`_ for the list of resolved issues
 in this release.
 
 .. _PyMongo 4.0 release notes in JIRA: https://jira.mongodb.org/secure/ReleaseNote.jspa?projectId=10004&version=18463
+.. _DBRef specification: https://github.com/mongodb/specifications/blob/5a8c8d7/source/dbref.rst
 
 Changes in Version 3.12.0
 -------------------------
diff --git a/doc/migrate-to-pymongo4.rst b/doc/migrate-to-pymongo4.rst
index 2394f29ca..0e512da77 100644
--- a/doc/migrate-to-pymongo4.rst
+++ b/doc/migrate-to-pymongo4.rst
@@ -752,3 +752,16 @@ Name is a required argument for pymongo.driver_info.DriverInfo
 
 ``name`` is now a required argument for the :class:`pymongo.driver_info.DriverInfo` class.
 
+DBRef BSON/JSON decoding behavior
+.................................
+
+Changed the BSON and JSON decoding behavior of :class:`~bson.dbref.DBRef`
+to match the behavior outlined in the `DBRef specification`_ version 1.0.
+Specifically, PyMongo now only decodes a subdocument into a
+:class:`~bson.dbref.DBRef` if and only if, it contains both ``$ref`` and
+``$id`` fields and the ``$ref``, ``$id``, and ``$db`` fields are of the
+correct type. Otherwise the document is returned as normal. Previously, any
+subdocument containing a ``$ref`` field would be decoded as a
+:class:`~bson.dbref.DBRef`.
+
+.. _DBRef specification: https://github.com/mongodb/specifications/blob/5a8c8d7/source/dbref.rst
diff --git a/test/bson_corpus/binary.json b/test/bson_corpus/binary.json
index 324c56abd..beb2e07a7 100644
--- a/test/bson_corpus/binary.json
+++ b/test/bson_corpus/binary.json
@@ -50,6 +50,11 @@
             "canonical_bson": "1D000000057800100000000573FFD26444B34C6990E8E7D1DFC035D400",
             "canonical_extjson": "{\"x\" : { \"$binary\" : {\"base64\" : \"c//SZESzTGmQ6OfR38A11A==\", \"subType\" : \"05\"}}}"
         },
+        {
+            "description": "subtype 0x07",
+            "canonical_bson": "1D000000057800100000000773FFD26444B34C6990E8E7D1DFC035D400",
+            "canonical_extjson": "{\"x\" : { \"$binary\" : {\"base64\" : \"c//SZESzTGmQ6OfR38A11A==\", \"subType\" : \"07\"}}}"
+        },
         {
             "description": "subtype 0x80",
             "canonical_bson": "0F0000000578000200000080FFFF00",
@@ -94,8 +99,20 @@
             "string": "{\"x\" : { \"$uuid\" : { \"data\" : \"73ffd264-44b3-4c69-90e8-e7d1dfc035d4\"}}}"
         },
         {
-            "description": "$uuid invalid value",
+            "description": "$uuid invalid value--too short",
             "string": "{\"x\" : { \"$uuid\" : \"73ffd264-44b3-90e8-e7d1dfc035d4\"}}"
+        },
+        {
+            "description": "$uuid invalid value--too long",
+            "string": "{\"x\" : { \"$uuid\" : \"73ffd264-44b3-4c69-90e8-e7d1dfc035d4-789e4\"}}"
+        },
+        {
+            "description": "$uuid invalid value--misplaced hyphens",
+            "string": "{\"x\" : { \"$uuid\" : \"73ff-d26444b-34c6-990e8e-7d1dfc035d4\"}}"
+        },
+        {
+            "description": "$uuid invalid value--too many hyphens",
+            "string": "{\"x\" : { \"$uuid\" : \"----d264-44b3-4--9-90e8-e7d1dfc0----\"}}"
         }
     ]
 }
diff --git a/test/bson_corpus/code.json b/test/bson_corpus/code.json
index 6f37349ad..b8482b254 100644
--- a/test/bson_corpus/code.json
+++ b/test/bson_corpus/code.json
@@ -20,48 +20,48 @@
         },
         {
             "description": "two-byte UTF-8 (\u00e9)",
-            "canonical_bson": "190000000261000D000000C3A9C3A9C3A9C3A9C3A9C3A90000",
-            "canonical_extjson": "{\"a\" : \"\\u00e9\\u00e9\\u00e9\\u00e9\\u00e9\\u00e9\"}"
+            "canonical_bson": "190000000D61000D000000C3A9C3A9C3A9C3A9C3A9C3A90000",
+            "canonical_extjson": "{\"a\" : {\"$code\" : \"\\u00e9\\u00e9\\u00e9\\u00e9\\u00e9\\u00e9\"}}"
         },
         {
             "description": "three-byte UTF-8 (\u2606)",
-            "canonical_bson": "190000000261000D000000E29886E29886E29886E298860000",
-            "canonical_extjson": "{\"a\" : \"\\u2606\\u2606\\u2606\\u2606\"}"
+            "canonical_bson": "190000000D61000D000000E29886E29886E29886E298860000",
+            "canonical_extjson": "{\"a\" : {\"$code\" : \"\\u2606\\u2606\\u2606\\u2606\"}}"
         },
         {
             "description": "Embedded nulls",
-            "canonical_bson": "190000000261000D0000006162006261620062616261620000",
-            "canonical_extjson": "{\"a\" : \"ab\\u0000bab\\u0000babab\"}"
+            "canonical_bson": "190000000D61000D0000006162006261620062616261620000",
+            "canonical_extjson": "{\"a\" : {\"$code\" : \"ab\\u0000bab\\u0000babab\"}}"
         }
     ],
     "decodeErrors": [
         {
             "description": "bad code string length: 0 (but no 0x00 either)",
-            "bson": "0C0000000261000000000000"
+            "bson": "0C0000000D61000000000000"
         },
         {
             "description": "bad code string length: -1",
-            "bson": "0C000000026100FFFFFFFF00"
+            "bson": "0C0000000D6100FFFFFFFF00"
         },
         {
             "description": "bad code string length: eats terminator",
-            "bson": "10000000026100050000006200620000"
+            "bson": "100000000D6100050000006200620000"
         },
         {
             "description": "bad code string length: longer than rest of document",
-            "bson": "120000000200FFFFFF00666F6F6261720000"
+            "bson": "120000000D00FFFFFF00666F6F6261720000"
         },
         {
             "description": "code string is not null-terminated",
-            "bson": "1000000002610004000000616263FF00"
+            "bson": "100000000D610004000000616263FF00"
         },
         {
             "description": "empty code string, but extra null",
-            "bson": "0E00000002610001000000000000"
+            "bson": "0E0000000D610001000000000000"
         },
         {
             "description": "invalid UTF-8",
-            "bson": "0E00000002610002000000E90000"
+            "bson": "0E0000000D610002000000E90000"
         }
     ]
 }
diff --git a/test/bson_corpus/dbref.json b/test/bson_corpus/dbref.json
index 1fe12c6f6..41c0b09d0 100644
--- a/test/bson_corpus/dbref.json
+++ b/test/bson_corpus/dbref.json
@@ -1,5 +1,5 @@
 {
-    "description": "DBRef",
+    "description": "Document type (DBRef sub-documents)",
     "bson_type": "0x03",
     "valid": [
         {
@@ -26,6 +26,26 @@
             "description": "Document with key names similar to those of a DBRef",
             "canonical_bson": "3e0000000224726566000c0000006e6f742d612d646272656600072469640058921b3e6e32ab156a22b59e022462616e616e6100050000007065656c0000",
             "canonical_extjson": "{\"$ref\": \"not-a-dbref\", \"$id\": {\"$oid\": \"58921b3e6e32ab156a22b59e\"}, \"$banana\": \"peel\"}"
+        },
+        {
+            "description": "DBRef with additional dollar-prefixed and dotted fields",
+            "canonical_bson": "48000000036462726566003c0000000224726566000b000000636f6c6c656374696f6e00072469640058921b3e6e32ab156a22b59e10612e62000100000010246300010000000000",
+            "canonical_extjson": "{\"dbref\": {\"$ref\": \"collection\", \"$id\": {\"$oid\": \"58921b3e6e32ab156a22b59e\"}, \"a.b\": {\"$numberInt\": \"1\"}, \"$c\": {\"$numberInt\": \"1\"}}}"
+        },
+        {
+            "description": "Sub-document resembles DBRef but $id is missing",
+            "canonical_bson": "26000000036462726566001a0000000224726566000b000000636f6c6c656374696f6e000000",
+            "canonical_extjson": "{\"dbref\": {\"$ref\": \"collection\"}}"
+        },
+        {
+            "description": "Sub-document resembles DBRef but $ref is not a string",
+            "canonical_bson": "2c000000036462726566002000000010247265660001000000072469640058921b3e6e32ab156a22b59e0000",
+            "canonical_extjson": "{\"dbref\": {\"$ref\": {\"$numberInt\": \"1\"}, \"$id\": {\"$oid\": \"58921b3e6e32ab156a22b59e\"}}}"
+        },
+        {
+            "description": "Sub-document resembles DBRef but $db is not a string",
+            "canonical_bson": "4000000003646272656600340000000224726566000b000000636f6c6c656374696f6e00072469640058921b3e6e32ab156a22b59e1024646200010000000000",
+            "canonical_extjson": "{\"dbref\": {\"$ref\": \"collection\", \"$id\": {\"$oid\": \"58921b3e6e32ab156a22b59e\"}, \"$db\": {\"$numberInt\": \"1\"}}}"
         }
     ]
 }
diff --git a/test/bson_corpus/double.json b/test/bson_corpus/double.json
index 7be4ff45e..d5b8fb3d7 100644
--- a/test/bson_corpus/double.json
+++ b/test/bson_corpus/double.json
@@ -30,13 +30,13 @@
         {
             "description": "1.2345678921232E+18",
             "canonical_bson": "100000000164002a1bf5f41022b14300",
-            "canonical_extjson": "{\"d\" : {\"$numberDouble\": \"1.2345678921232e+18\"}}",
+            "canonical_extjson": "{\"d\" : {\"$numberDouble\": \"1.2345678921232E+18\"}}",
             "relaxed_extjson": "{\"d\" : 1.2345678921232E+18}"
         },
         {
             "description": "-1.2345678921232E+18",
             "canonical_bson": "100000000164002a1bf5f41022b1c300",
-            "canonical_extjson": "{\"d\" : {\"$numberDouble\": \"-1.2345678921232e+18\"}}",
+            "canonical_extjson": "{\"d\" : {\"$numberDouble\": \"-1.2345678921232E+18\"}}",
             "relaxed_extjson": "{\"d\" : -1.2345678921232E+18}"
         },
         {
diff --git a/test/bson_corpus/symbol.json b/test/bson_corpus/symbol.json
index 4e46cb951..3dd3577eb 100644
--- a/test/bson_corpus/symbol.json
+++ b/test/bson_corpus/symbol.json
@@ -50,31 +50,31 @@
     "decodeErrors": [
         {
             "description": "bad symbol length: 0 (but no 0x00 either)",
-            "bson": "0C0000000261000000000000"
+            "bson": "0C0000000E61000000000000"
         },
         {
             "description": "bad symbol length: -1",
-            "bson": "0C000000026100FFFFFFFF00"
+            "bson": "0C0000000E6100FFFFFFFF00"
         },
         {
             "description": "bad symbol length: eats terminator",
-            "bson": "10000000026100050000006200620000"
+            "bson": "100000000E6100050000006200620000"
         },
         {
             "description": "bad symbol length: longer than rest of document",
-            "bson": "120000000200FFFFFF00666F6F6261720000"
+            "bson": "120000000E00FFFFFF00666F6F6261720000"
         },
         {
             "description": "symbol is not null-terminated",
-            "bson": "1000000002610004000000616263FF00"
+            "bson": "100000000E610004000000616263FF00"
         },
         {
             "description": "empty symbol, but extra null",
-            "bson": "0E00000002610001000000000000"
+            "bson": "0E0000000E610001000000000000"
         },
         {
             "description": "invalid UTF-8",
-            "bson": "0E00000002610002000000E90000"
+            "bson": "0E0000000E610002000000E90000"
         }
     ]
 }
diff --git a/test/crud/unified/aggregate-merge.json b/test/crud/unified/aggregate-merge.json
index c34e93a69..ac61ceb8a 100644
--- a/test/crud/unified/aggregate-merge.json
+++ b/test/crud/unified/aggregate-merge.json
@@ -1,6 +1,6 @@
 {
   "description": "aggregate-merge",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.1.11"
diff --git a/test/crud/unified/bulkWrite-arrayFilters-clientError.json b/test/crud/unified/bulkWrite-arrayFilters-clientError.json
index 6073890dd..63815e323 100644
--- a/test/crud/unified/bulkWrite-arrayFilters-clientError.json
+++ b/test/crud/unified/bulkWrite-arrayFilters-clientError.json
@@ -1,6 +1,6 @@
 {
   "description": "bulkWrite-arrayFilters-clientError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "maxServerVersion": "3.5.5"
diff --git a/test/crud/unified/bulkWrite-arrayFilters.json b/test/crud/unified/bulkWrite-arrayFilters.json
index 4d7b4b794..70ee014f7 100644
--- a/test/crud/unified/bulkWrite-arrayFilters.json
+++ b/test/crud/unified/bulkWrite-arrayFilters.json
@@ -1,6 +1,6 @@
 {
   "description": "bulkWrite-arrayFilters",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "3.5.6"
diff --git a/test/crud/unified/bulkWrite-delete-hint-clientError.json b/test/crud/unified/bulkWrite-delete-hint-clientError.json
index c55067be2..2961b55dc 100644
--- a/test/crud/unified/bulkWrite-delete-hint-clientError.json
+++ b/test/crud/unified/bulkWrite-delete-hint-clientError.json
@@ -1,6 +1,6 @@
 {
   "description": "bulkWrite-delete-hint-clientError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "maxServerVersion": "3.3.99"
diff --git a/test/crud/unified/bulkWrite-delete-hint-serverError.json b/test/crud/unified/bulkWrite-delete-hint-serverError.json
index 30b9010ac..fa9952209 100644
--- a/test/crud/unified/bulkWrite-delete-hint-serverError.json
+++ b/test/crud/unified/bulkWrite-delete-hint-serverError.json
@@ -1,6 +1,6 @@
 {
   "description": "bulkWrite-delete-hint-serverError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "3.4.0",
diff --git a/test/crud/unified/bulkWrite-delete-hint.json b/test/crud/unified/bulkWrite-delete-hint.json
index 31f386532..9fcdecefd 100644
--- a/test/crud/unified/bulkWrite-delete-hint.json
+++ b/test/crud/unified/bulkWrite-delete-hint.json
@@ -1,6 +1,6 @@
 {
   "description": "bulkWrite-delete-hint",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.3.4"
diff --git a/test/crud/unified/bulkWrite-update-hint-clientError.json b/test/crud/unified/bulkWrite-update-hint-clientError.json
index 68a92065a..d5eb71c29 100644
--- a/test/crud/unified/bulkWrite-update-hint-clientError.json
+++ b/test/crud/unified/bulkWrite-update-hint-clientError.json
@@ -1,6 +1,6 @@
 {
   "description": "bulkWrite-update-hint-clientError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "maxServerVersion": "3.3.99"
diff --git a/test/crud/unified/bulkWrite-update-hint-serverError.json b/test/crud/unified/bulkWrite-update-hint-serverError.json
index 2a9a6795c..b0f7e1b38 100644
--- a/test/crud/unified/bulkWrite-update-hint-serverError.json
+++ b/test/crud/unified/bulkWrite-update-hint-serverError.json
@@ -1,6 +1,6 @@
 {
   "description": "bulkWrite-update-hint-serverError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "3.4.0",
diff --git a/test/crud/unified/bulkWrite-update-hint.json b/test/crud/unified/bulkWrite-update-hint.json
index b8445d80d..420635989 100644
--- a/test/crud/unified/bulkWrite-update-hint.json
+++ b/test/crud/unified/bulkWrite-update-hint.json
@@ -1,6 +1,6 @@
 {
   "description": "bulkWrite-update-hint",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.2.0"
diff --git a/test/crud/unified/deleteMany-hint-clientError.json b/test/crud/unified/deleteMany-hint-clientError.json
index 285f567f0..66320122b 100644
--- a/test/crud/unified/deleteMany-hint-clientError.json
+++ b/test/crud/unified/deleteMany-hint-clientError.json
@@ -1,6 +1,6 @@
 {
   "description": "deleteMany-hint-clientError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "maxServerVersion": "3.3.99"
diff --git a/test/crud/unified/deleteMany-hint-serverError.json b/test/crud/unified/deleteMany-hint-serverError.json
index 90bfb89fc..88d4a6557 100644
--- a/test/crud/unified/deleteMany-hint-serverError.json
+++ b/test/crud/unified/deleteMany-hint-serverError.json
@@ -1,6 +1,6 @@
 {
   "description": "deleteMany-hint-serverError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "3.4.0",
diff --git a/test/crud/unified/deleteMany-hint.json b/test/crud/unified/deleteMany-hint.json
index b0cdc0304..59d903d20 100644
--- a/test/crud/unified/deleteMany-hint.json
+++ b/test/crud/unified/deleteMany-hint.json
@@ -1,6 +1,6 @@
 {
   "description": "deleteMany-hint",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.3.4"
diff --git a/test/crud/unified/deleteOne-hint-clientError.json b/test/crud/unified/deleteOne-hint-clientError.json
index b6b2932bd..cf629f59e 100644
--- a/test/crud/unified/deleteOne-hint-clientError.json
+++ b/test/crud/unified/deleteOne-hint-clientError.json
@@ -1,6 +1,6 @@
 {
   "description": "deleteOne-hint-clientError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "maxServerVersion": "3.3.99"
diff --git a/test/crud/unified/deleteOne-hint-serverError.json b/test/crud/unified/deleteOne-hint-serverError.json
index 8b1398c75..15541ed85 100644
--- a/test/crud/unified/deleteOne-hint-serverError.json
+++ b/test/crud/unified/deleteOne-hint-serverError.json
@@ -1,6 +1,6 @@
 {
   "description": "deleteOne-hint-serverError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "3.4.0",
diff --git a/test/crud/unified/deleteOne-hint.json b/test/crud/unified/deleteOne-hint.json
index 9e3970a54..bcc4bc234 100644
--- a/test/crud/unified/deleteOne-hint.json
+++ b/test/crud/unified/deleteOne-hint.json
@@ -1,6 +1,6 @@
 {
   "description": "deleteOne-hint",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.3.4"
diff --git a/test/crud/unified/find-allowdiskuse-clientError.json b/test/crud/unified/find-allowdiskuse-clientError.json
index a47fd8e25..5bd954e79 100644
--- a/test/crud/unified/find-allowdiskuse-clientError.json
+++ b/test/crud/unified/find-allowdiskuse-clientError.json
@@ -1,6 +1,6 @@
 {
   "description": "find-allowdiskuse-clientError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "maxServerVersion": "3.0.99"
diff --git a/test/crud/unified/find-allowdiskuse-serverError.json b/test/crud/unified/find-allowdiskuse-serverError.json
index a7907ba25..dc58f8f0e 100644
--- a/test/crud/unified/find-allowdiskuse-serverError.json
+++ b/test/crud/unified/find-allowdiskuse-serverError.json
@@ -1,6 +1,6 @@
 {
   "description": "find-allowdiskuse-serverError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "3.2",
diff --git a/test/crud/unified/find-allowdiskuse.json b/test/crud/unified/find-allowdiskuse.json
index 8d4cf66bf..789bb7fbf 100644
--- a/test/crud/unified/find-allowdiskuse.json
+++ b/test/crud/unified/find-allowdiskuse.json
@@ -1,6 +1,6 @@
 {
   "description": "find-allowdiskuse",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.3.1"
diff --git a/test/crud/unified/findOneAndDelete-hint-clientError.json b/test/crud/unified/findOneAndDelete-hint-clientError.json
index d04125edd..c6ff46786 100644
--- a/test/crud/unified/findOneAndDelete-hint-clientError.json
+++ b/test/crud/unified/findOneAndDelete-hint-clientError.json
@@ -1,6 +1,6 @@
 {
   "description": "findOneAndDelete-hint-clientError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "maxServerVersion": "4.0.99"
diff --git a/test/crud/unified/findOneAndDelete-hint-serverError.json b/test/crud/unified/findOneAndDelete-hint-serverError.json
index 23c01f48f..b87410272 100644
--- a/test/crud/unified/findOneAndDelete-hint-serverError.json
+++ b/test/crud/unified/findOneAndDelete-hint-serverError.json
@@ -1,6 +1,6 @@
 {
   "description": "findOneAndDelete-hint-serverError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.2.0",
diff --git a/test/crud/unified/findOneAndDelete-hint.json b/test/crud/unified/findOneAndDelete-hint.json
index 0180010dc..8b53f2bd3 100644
--- a/test/crud/unified/findOneAndDelete-hint.json
+++ b/test/crud/unified/findOneAndDelete-hint.json
@@ -1,6 +1,6 @@
 {
   "description": "findOneAndDelete-hint",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.3.4"
diff --git a/test/crud/unified/findOneAndReplace-hint-clientError.json b/test/crud/unified/findOneAndReplace-hint-clientError.json
index c483b2302..6b07eb1f4 100644
--- a/test/crud/unified/findOneAndReplace-hint-clientError.json
+++ b/test/crud/unified/findOneAndReplace-hint-clientError.json
@@ -1,6 +1,6 @@
 {
   "description": "findOneAndReplace-hint-clientError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "maxServerVersion": "4.0.99"
diff --git a/test/crud/unified/findOneAndReplace-hint-serverError.json b/test/crud/unified/findOneAndReplace-hint-serverError.json
index e8f1c8936..7fbf5a0ea 100644
--- a/test/crud/unified/findOneAndReplace-hint-serverError.json
+++ b/test/crud/unified/findOneAndReplace-hint-serverError.json
@@ -1,6 +1,6 @@
 {
   "description": "findOneAndReplace-hint-serverError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.2.0",
diff --git a/test/crud/unified/findOneAndReplace-hint.json b/test/crud/unified/findOneAndReplace-hint.json
index 13ac6a9c9..d07c5921a 100644
--- a/test/crud/unified/findOneAndReplace-hint.json
+++ b/test/crud/unified/findOneAndReplace-hint.json
@@ -1,6 +1,6 @@
 {
   "description": "findOneAndReplace-hint",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.3.1"
diff --git a/test/crud/unified/findOneAndUpdate-hint-clientError.json b/test/crud/unified/findOneAndUpdate-hint-clientError.json
index dace72b0a..d0b51313c 100644
--- a/test/crud/unified/findOneAndUpdate-hint-clientError.json
+++ b/test/crud/unified/findOneAndUpdate-hint-clientError.json
@@ -1,6 +1,6 @@
 {
   "description": "findOneAndUpdate-hint-clientError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "maxServerVersion": "4.0.99"
diff --git a/test/crud/unified/findOneAndUpdate-hint-serverError.json b/test/crud/unified/findOneAndUpdate-hint-serverError.json
index 1413ced2e..99fd9938f 100644
--- a/test/crud/unified/findOneAndUpdate-hint-serverError.json
+++ b/test/crud/unified/findOneAndUpdate-hint-serverError.json
@@ -1,6 +1,6 @@
 {
   "description": "findOneAndUpdate-hint-serverError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.2.0",
diff --git a/test/crud/unified/findOneAndUpdate-hint.json b/test/crud/unified/findOneAndUpdate-hint.json
index 68cef18ef..5be6d2b3e 100644
--- a/test/crud/unified/findOneAndUpdate-hint.json
+++ b/test/crud/unified/findOneAndUpdate-hint.json
@@ -1,6 +1,6 @@
 {
   "description": "findOneAndUpdate-hint",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.3.1"
diff --git a/test/crud/unified/replaceOne-hint.json b/test/crud/unified/replaceOne-hint.json
index edb1ceb7c..6926e9d8d 100644
--- a/test/crud/unified/replaceOne-hint.json
+++ b/test/crud/unified/replaceOne-hint.json
@@ -1,6 +1,6 @@
 {
   "description": "replaceOne-hint",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.2.0"
diff --git a/test/crud/unified/updateMany-hint-clientError.json b/test/crud/unified/updateMany-hint-clientError.json
index 99c66c919..5da878e29 100644
--- a/test/crud/unified/updateMany-hint-clientError.json
+++ b/test/crud/unified/updateMany-hint-clientError.json
@@ -1,6 +1,6 @@
 {
   "description": "updateMany-hint-clientError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "maxServerVersion": "3.3.99"
diff --git a/test/crud/unified/updateMany-hint-serverError.json b/test/crud/unified/updateMany-hint-serverError.json
index cc5ecfe26..c81f36b13 100644
--- a/test/crud/unified/updateMany-hint-serverError.json
+++ b/test/crud/unified/updateMany-hint-serverError.json
@@ -1,6 +1,6 @@
 {
   "description": "updateMany-hint-serverError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "3.4.0",
diff --git a/test/crud/unified/updateMany-hint.json b/test/crud/unified/updateMany-hint.json
index e5f707fb5..929be5299 100644
--- a/test/crud/unified/updateMany-hint.json
+++ b/test/crud/unified/updateMany-hint.json
@@ -1,6 +1,6 @@
 {
   "description": "updateMany-hint",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.2.0"
diff --git a/test/crud/unified/updateOne-hint-clientError.json b/test/crud/unified/updateOne-hint-clientError.json
index 8c0ddbd1d..d4f1a5343 100644
--- a/test/crud/unified/updateOne-hint-clientError.json
+++ b/test/crud/unified/updateOne-hint-clientError.json
@@ -1,6 +1,6 @@
 {
   "description": "updateOne-hint-clientError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "maxServerVersion": "3.3.99"
diff --git a/test/crud/unified/updateOne-hint-serverError.json b/test/crud/unified/updateOne-hint-serverError.json
index d8a46da94..05fb03331 100644
--- a/test/crud/unified/updateOne-hint-serverError.json
+++ b/test/crud/unified/updateOne-hint-serverError.json
@@ -1,6 +1,6 @@
 {
   "description": "updateOne-hint-serverError",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "3.4.0",
diff --git a/test/crud/unified/updateOne-hint.json b/test/crud/unified/updateOne-hint.json
index 9277c605f..484e00757 100644
--- a/test/crud/unified/updateOne-hint.json
+++ b/test/crud/unified/updateOne-hint.json
@@ -1,6 +1,6 @@
 {
   "description": "updateOne-hint",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.2.0"
diff --git a/test/crud/unified/updateWithPipelines.json b/test/crud/unified/updateWithPipelines.json
index 12ae04665..164f2f6a1 100644
--- a/test/crud/unified/updateWithPipelines.json
+++ b/test/crud/unified/updateWithPipelines.json
@@ -1,6 +1,6 @@
 {
   "description": "updateWithPipelines",
-  "schemaVersion": "1.1",
+  "schemaVersion": "1.0",
   "runOnRequirements": [
     {
       "minServerVersion": "4.1.11"
diff --git a/test/test_bson.py b/test/test_bson.py
index ee30c8948..89f4a1117 100644
--- a/test/test_bson.py
+++ b/test/test_bson.py
@@ -490,8 +490,7 @@ class TestBSON(unittest.TestCase):
         ref_only = {'ref': {'$ref': 'collection'}}
         id_only = {'ref': {'$id': ObjectId()}}
 
-        self.assertEqual(DBRef('collection', id=None),
-                         decode(encode(ref_only))['ref'])
+        self.assertEqual(ref_only, decode(encode(ref_only)))
         self.assertEqual(id_only, decode(encode(id_only)))
 
     def test_bytes_as_keys(self):
diff --git a/test/test_bson_corpus.py b/test/test_bson_corpus.py
index 68703cc70..7893395c6 100644
--- a/test/test_bson_corpus.py
+++ b/test/test_bson_corpus.py
@@ -40,20 +40,27 @@ from test import unittest
 _TEST_PATH = os.path.join(
     os.path.dirname(os.path.realpath(__file__)), 'bson_corpus')
 
-_TESTS_TO_SKIP = set([
+_TESTS_TO_SKIP = {
     # Python cannot decode dates after year 9999.
     'Y10K',
-])
+}
 
-_NON_PARSE_ERRORS = set([
+_NON_PARSE_ERRORS = {
     # {"$date": <number>} is our legacy format which we still need to parse.
     'Bad $date (number, not string or hash)',
     # This variant of $numberLong may have been generated by an old version
     # of mongoexport.
     'Bad $numberLong (number, not string)',
+    # Python's UUID constructor is very permissive.
+    '$uuid invalid value--misplaced hyphens',
     # We parse Regex flags with extra characters, including nulls.
     'Null byte in $regularExpression options',
-])
+}
+
+_IMPLCIT_LOSSY_TESTS = {
+    # JSON decodes top-level $ref+$id as a DBRef but BSON doesn't.
+    'Document with key names similar to those of a DBRef'
+}
 
 _DEPRECATED_BSON_TYPES = {
     # Symbol
@@ -128,15 +135,22 @@ def create_test(case_spec):
             cEJ = valid_case['canonical_extjson']
             rEJ = valid_case.get('relaxed_extjson')
             dEJ = valid_case.get('degenerate_extjson')
+            if description in _IMPLCIT_LOSSY_TESTS:
+                valid_case.setdefault('lossy', True)
             lossy = valid_case.get('lossy')
 
+            # BSON double, use lowercase 'e+' to match Python's encoding
+            if bson_type == '0x01':
+                cEJ = cEJ.replace('E+', 'e+')
+
             decoded_bson = decode_bson(cB)
 
             if not lossy:
                 # Make sure we can parse the legacy (default) JSON format.
                 legacy_json = json_util.dumps(
                     decoded_bson, json_options=json_util.LEGACY_JSON_OPTIONS)
-                self.assertEqual(decode_extjson(legacy_json), decoded_bson)
+                self.assertEqual(
+                    decode_extjson(legacy_json), decoded_bson, description)
 
             if deprecated:
                 if 'converted_bson' in valid_case:
@@ -158,7 +172,7 @@ def create_test(case_spec):
             if not (sys.platform.startswith("java") and
                     description == 'NaN with payload'):
                 # Test round-tripping canonical bson.
-                self.assertEqual(encode_bson(decoded_bson), cB)
+                self.assertEqual(encode_bson(decoded_bson), cB, description)
             self.assertJsonEqual(encode_extjson(decoded_bson), cEJ)
 
             # Test round-tripping canonical extended json.
@@ -191,24 +205,24 @@ def create_test(case_spec):
                     binascii.unhexlify(decode_error_case['bson'].encode('utf8')))
 
         for parse_error_case in case_spec.get('parseErrors', []):
+            description = parse_error_case['description']
+            if description in _NON_PARSE_ERRORS:
+                decode_extjson(parse_error_case['string'])
+                continue
             if bson_type == '0x13':
                 self.assertRaises(
                     DecimalException, Decimal128, parse_error_case['string'])
             elif bson_type == '0x00':
-                description = parse_error_case['description']
-                if description in _NON_PARSE_ERRORS:
-                    decode_extjson(parse_error_case['string'])
-                else:
-                    try:
-                        doc = decode_extjson(parse_error_case['string'])
-                        # Null bytes are validated when encoding to BSON.
-                        if 'Null' in description:
-                            to_bson(doc)
-                        raise AssertionError('exception not raised for test '
-                                             'case: ' + description)
-                    except (ValueError, KeyError, TypeError, InvalidId,
-                            InvalidDocument):
-                        pass
+                try:
+                    doc = decode_extjson(parse_error_case['string'])
+                    # Null bytes are validated when encoding to BSON.
+                    if 'Null' in description:
+                        to_bson(doc)
+                    raise AssertionError('exception not raised for test '
+                                         'case: ' + description)
+                except (ValueError, KeyError, TypeError, InvalidId,
+                        InvalidDocument):
+                    pass
             elif bson_type == '0x05':
                 try:
                     decode_extjson(parse_error_case['string'])
diff --git a/test/test_dbref.py b/test/test_dbref.py
index d71c2c68e..964947351 100644
--- a/test/test_dbref.py
+++ b/test/test_dbref.py
@@ -18,6 +18,7 @@ import pickle
 import sys
 sys.path[0:0] = [""]
 
+from bson import encode, decode
 from bson.dbref import DBRef
 from bson.objectid import ObjectId
 from test import unittest
@@ -131,5 +132,108 @@ class TestDBRef(unittest.TestCase):
 
         self.assertNotEqual(hash(dbref_1a), hash(dbref_2a))
 
+
+# https://github.com/mongodb/specifications/blob/master/source/dbref.rst#test-plan
+class TestDBRefSpec(unittest.TestCase):
+    def test_decoding_1_2_3(self):
+        for doc in [
+            # 1, Valid documents MUST be decoded to a DBRef:
+            {"$ref": "coll0", "$id": ObjectId("60a6fe9a54f4180c86309efa")},
+            {"$ref": "coll0", "$id": 1},
+            {"$ref": "coll0", "$id": None},
+            {"$ref": "coll0", "$id": 1, "$db": "db0"},
+            # 2, Valid documents with extra fields:
+            {"$ref": "coll0", "$id": 1, "$db": "db0", "foo": "bar"},
+            {"$ref": "coll0", "$id": 1, "foo": True, "bar": False},
+            {"$ref": "coll0", "$id": 1, "meta": {"foo": 1, "bar": 2}},
+            {"$ref": "coll0", "$id": 1, "$foo": "bar"},
+            {"$ref": "coll0", "$id": 1, "foo.bar": 0},
+            # 3, Valid documents with out of order fields:
+            {"$id": 1, "$ref": "coll0"},
+            {"$db": "db0", "$ref": "coll0", "$id": 1},
+            {"foo": 1, "$id": 1, "$ref": "coll0"},
+            {"foo": 1, "$ref": "coll0", "$id": 1, "$db": "db0"},
+            {"foo": 1, "$ref": "coll0", "$id": 1, "$db": "db0", "bar": 1},
+        ]:
+            with self.subTest(doc=doc):
+                decoded = decode(encode({'dbref': doc}))
+                dbref = decoded['dbref']
+                self.assertIsInstance(dbref, DBRef)
+                self.assertEqual(dbref.collection, doc['$ref'])
+                self.assertEqual(dbref.id, doc['$id'])
+                self.assertEqual(dbref.database, doc.get('$db'))
+                for extra in set(doc.keys()) - {"$ref", "$id", "$db"}:
+                    self.assertEqual(getattr(dbref, extra), doc[extra])
+
+    def test_decoding_4_5(self):
+        for doc in [
+            # 4, Documents missing required fields MUST NOT be decoded to a
+            # DBRef:
+            {"$ref": "coll0"},
+            {"$id": ObjectId("60a6fe9a54f4180c86309efa")},
+            {"$db": "db0"},
+            # 5, Documents with invalid types for $ref or $db MUST NOT be
+            # decoded to a DBRef
+            {"$ref": True, "$id": 1},
+            {"$ref": "coll0", "$id": 1, "$db": 1},
+        ]:
+            with self.subTest(doc=doc):
+                decoded = decode(encode({'dbref': doc}))
+                dbref = decoded['dbref']
+                self.assertIsInstance(dbref, dict)
+
+    def test_encoding_1_2(self):
+        for doc in [
+            # 1, Encoding DBRefs with basic fields:
+            {"$ref": "coll0", "$id": ObjectId("60a6fe9a54f4180c86309efa")},
+            {"$ref": "coll0", "$id": 1},
+            {"$ref": "coll0", "$id": None},
+            {"$ref": "coll0", "$id": 1, "$db": "db0"},
+            # 2, Encoding DBRefs with extra, optional fields:
+            {"$ref": "coll0", "$id": 1, "$db": "db0", "foo": "bar"},
+            {"$ref": "coll0", "$id": 1, "foo": True, "bar": False},
+            {"$ref": "coll0", "$id": 1, "meta": {"foo": 1, "bar": 2}},
+            {"$ref": "coll0", "$id": 1, "$foo": "bar"},
+            {"$ref": "coll0", "$id": 1, "foo.bar": 0},
+        ]:
+            with self.subTest(doc=doc):
+                # Decode the test input to a DBRef via a BSON roundtrip.
+                encoded_doc = encode({'dbref': doc})
+                decoded = decode(encoded_doc)
+                dbref = decoded['dbref']
+                self.assertIsInstance(dbref, DBRef)
+                # Encode the DBRef.
+                encoded_dbref = encode(decoded)
+                self.assertEqual(encoded_dbref, encoded_doc)
+                # Ensure extra fields are present.
+                for extra in set(doc.keys()) - {"$ref", "$id", "$db"}:
+                    self.assertEqual(getattr(dbref, extra), doc[extra])
+
+    def test_encoding_3(self):
+        for doc in [
+            # 3, Encoding DBRefs re-orders any out of order fields during
+            # decoding:
+            {"$id": 1, "$ref": "coll0"},
+            {"$db": "db0", "$ref": "coll0", "$id": 1},
+            {"foo": 1, "$id": 1, "$ref": "coll0"},
+            {"foo": 1, "$ref": "coll0", "$id": 1, "$db": "db0"},
+            {"foo": 1, "$ref": "coll0", "$id": 1, "$db": "db0", "bar": 1},
+        ]:
+            with self.subTest(doc=doc):
+                # Decode the test input to a DBRef via a BSON roundtrip.
+                encoded_doc = encode({'dbref': doc})
+                decoded = decode(encoded_doc)
+                dbref = decoded['dbref']
+                self.assertIsInstance(dbref, DBRef)
+                # Encode the DBRef.
+                encoded_dbref = encode(decoded)
+                # BSON does not match because DBRef fields are reordered.
+                self.assertNotEqual(encoded_dbref, encoded_doc)
+                self.assertEqual(decode(encoded_dbref), decode(encoded_doc))
+                # Ensure extra fields are present.
+                for extra in set(doc.keys()) - {"$ref", "$id", "$db"}:
+                    self.assertEqual(getattr(dbref, extra), doc[extra])
+
+
 if __name__ == "__main__":
     unittest.main()