1 files changed, 44 insertions, 0 deletions
diff --git a/jstests/multiVersion/targetedTestsLastLtsFeatures/partial_indexes_downgrade.js b/jstests/multiVersion/targetedTestsLastLtsFeatures/partial_indexes_downgrade.js
new file mode 100644
index 00000000000..95eb03bfeb5
--- /dev/null
+++ b/jstests/multiVersion/targetedTestsLastLtsFeatures/partial_indexes_downgrade.js
@@ -0,0 +1,44 @@
+/**
+ * Tests that we don't fail the FCV check for partial indexes on the admin database during startup.
+ */
+
+(function() {
+'use strict';
+
+const dbpath = MongoRunner.dataPath + 'partial_indexes_downgrade';
+resetDbpath(dbpath);
+
+// If we have a partial index on the admin database, we want to make sure we can startup properly
+// despite FCV not being initialized yet. It's possible to hit an invariant if featureFlag.isEnabled
+// is called without checking fcv.isVersionInitialized (see SERVER-71068 for more details).
+const dbName = 'admin';
+const collName = 'partial_indexes_downgrade';
+
+// Startup with latest, create partial index, stop mongod.
+{
+    const conn = MongoRunner.runMongod({dbpath: dbpath, binVersion: 'latest', noCleanData: true});
+    const db = conn.getDB(dbName);
+    const coll = db[collName];
+
+    assert.commandWorked(coll.createIndex(
+        {a: 1, b: 1}, {partialFilterExpression: {$or: [{a: {$lt: 20}}, {b: {$lt: 10}}]}}));
+
+    assert.commandWorked(coll.insert({a: 1, b: 1}));
+    assert.commandWorked(coll.insert({a: 30, b: 20}));
+
+    MongoRunner.stopMongod(conn);
+}
+
+// Startup with latest again, to make sure we're not checking FCV for this index at startup.
+{
+    const conn = MongoRunner.runMongod({dbpath: dbpath, binVersion: 'latest', noCleanData: true});
+    const db = conn.getDB(dbName);
+    const coll = db[collName];
+
+    // Make sure we are on the same db path as before.
+    assert.eq(coll.aggregate().toArray().length, 2);
+
+    assert.commandWorked(db.adminCommand({setFeatureCompatibilityVersion: lastLTSFCV}));
+    MongoRunner.stopMongod(conn);
+}
+})();