2 files changed, 21 insertions, 3 deletions
diff --git a/jstests/aggregation/sources/group/group_by_empty_object.js b/jstests/aggregation/sources/group/group_by_empty_object.js
new file mode 100644
index 00000000000..1dc64a6ee1c
--- /dev/null
+++ b/jstests/aggregation/sources/group/group_by_empty_object.js
@@ -0,0 +1,19 @@
+/*
+ * Test that $group works when an empty object is passed for _id. This is intended to reproduce
+ * SERVER-89611.
+ */
+const coll = db.group_by_empty_obj;
+coll.drop();
+
+assert.commandWorked(coll.insert([{_id: 1, x: 1}, {_id: 2, x: 2}]));
+
+function assertIsEmptyObjId(groupSpec) {
+    assert.eq([{_id: {}}], coll.aggregate([groupSpec]).toArray());
+}
+assertIsEmptyObjId({$group: {_id: {}}});
+assertIsEmptyObjId({$group: {_id: {$expr: {}}}});
+assertIsEmptyObjId({$group: {_id: {$expr: {$const: {}}}}});
+assertIsEmptyObjId({$group: {_id: {$expr: {$expr: {}}}}});
+
+// The original fuzzer failure involved a $sortByCount query
+assert.eq([{_id: {}, count: 2}], coll.aggregate([{$sortByCount: {$expr: {}}}]).toArray());
diff --git a/jstests/aggregation/sources/group/group_by_variable.js b/jstests/aggregation/sources/group/group_by_variable.js
index ef08d7bb91b..f306a8eabd0 100644
--- a/jstests/aggregation/sources/group/group_by_variable.js
+++ b/jstests/aggregation/sources/group/group_by_variable.js
@@ -5,8 +5,7 @@
 const coll = db.group_by_system_var;
 coll.drop();
 
-assert.commandWorked(coll.insert({_id: 1, x: 1}));
-assert.commandWorked(coll.insert({_id: 2, x: 2}));
+assert.commandWorked(coll.insert([{_id: 1, x: 1}, {_id: 2, x: 2}]));
 
 function checkPipeline(pipeline, expectedResults) {
     const res = coll.aggregate(pipeline).toArray();
@@ -19,4 +18,4 @@ checkPipeline([{$group: {_id: "$$CURRENT"}}, {$sort: {"_id": 1}}], wholeCollUnde
 
 const collIds = [{_id: 1}, {_id: 2}];
 checkPipeline([{$group: {_id: "$$ROOT.x"}}, {$sort: {"_id": 1}}], collIds);
-checkPipeline([{$group: {_id: "$$CURRENT.x"}}, {$sort: {"_id": 1}}], collIds);
-\ No newline at end of file
+checkPipeline([{$group: {_id: "$$CURRENT.x"}}, {$sort: {"_id": 1}}], collIds);