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diff --git a/jstests/sharding/change_streams_unsharded_update_resume.js b/jstests/sharding/change_streams_unsharded_update_resume.js
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+++ b/jstests/sharding/change_streams_unsharded_update_resume.js
@@ -0,0 +1,63 @@
+/**
+ * Tests that the post-image of an update which occurred while the collection was unsharded can
+ * still be looked up after the collection becomes sharded. Exercises the fix for SERVER-44484.
+ * @tags: [uses_change_streams, requires_fcv_44]
+ */
+(function() {
+"use strict";
+
+// Start a new sharded cluster with 2 nodes and obtain references to the test DB and collection.
+const st = new ShardingTest({
+    shards: 2,
+    mongos: 1,
+    rs: {nodes: 1, setParameter: {periodicNoopIntervalSecs: 1, writePeriodicNoops: true}}
+});
+
+const mongosDB = st.s0.getDB(jsTestName());
+const mongosColl = mongosDB.test;
+
+// Open a change stream on the unsharded collection.
+let csCur = mongosColl.watch([], {fullDocument: "updateLookup"});
+
+// Insert one document with a known _id into the unsharded collection, and obtain its resume token.
+assert.commandWorked(mongosColl.insert({_id: 0, a: -100}));
+assert.soon(() => csCur.hasNext());
+const insertEvent = csCur.next();
+assert.eq(insertEvent.operationType, "insert");
+
+// Update the document and confirm that we can see the updateLookup fullDocument.
+assert.commandWorked(mongosColl.update({_id: 0}, {$set: {updated: true}}));
+assert.soon(() => csCur.hasNext());
+let updateEvent = csCur.next();
+assert.eq(updateEvent.operationType, "update");
+assert.docEq(updateEvent.fullDocument, {_id: 0, a: -100, updated: true});
+
+// Now shard the collection on {a: 1} and move the upper chunk to the other shard.
+assert.commandWorked(mongosColl.createIndex({a: 1}));
+st.shardColl(mongosColl, {a: 1}, {a: 0}, {a: 0});
+
+// Resume a change stream just after the initial insert. We expect the update lookup to succeed,
+// despite the fact that only the _id and not the entire documentKey was recorded in the oplog.
+csCur = mongosColl.watch([], {resumeAfter: insertEvent._id, fullDocument: "updateLookup"});
+assert.soon(() => csCur.hasNext());
+updateEvent = csCur.next();
+assert.eq(updateEvent.operationType, "update");
+assert.docEq(updateEvent.fullDocument, {_id: 0, a: -100, updated: true});
+
+// Insert a second document with the same _id on the second shard.
+assert.commandWorked(mongosColl.insert({_id: 0, a: 100}));
+
+// Now that two documents with the same _id are present, the update lookup fails.
+csCur = mongosColl.watch([], {resumeAfter: insertEvent._id, fullDocument: "updateLookup"});
+assert.soon(() => {
+    try {
+        assert.eq(csCur.hasNext(), false, () => tojson(csCur.next()));
+        return false;
+    } catch (ex) {
+        assert.eq(ex.code, ErrorCodes.ChangeStreamFatalError);
+        return true;
+    }
+});
+
+st.stop();
+})();