1 files changed, 55 insertions, 0 deletions
diff --git a/jstests/noPassthroughWithMongod/isMaster_feature_compatibility_version.js b/jstests/noPassthroughWithMongod/isMaster_feature_compatibility_version.js
new file mode 100644
index 00000000000..53ef53bff5b
--- /dev/null
+++ b/jstests/noPassthroughWithMongod/isMaster_feature_compatibility_version.js
@@ -0,0 +1,55 @@
+// Tests that when the featureCompatibilityVersion is not equal to the downgrade version, running
+// isMaster with internalClient returns a response with minWireVersion=maxWireVersion. This ensures
+// that an older version mongod/mongos will fail to connect to the node when it is upgraded,
+// upgrading, or downgrading.
+(function() {
+    "use strict";
+
+    const adminDB = db.getSiblingDB("admin");
+    const isMasterCommand = {
+        isMaster: 1,
+        internalClient: {minWireVersion: NumberInt(0), maxWireVersion: NumberInt(6)}
+    };
+    const upgradeVersion = "3.6";
+    const downgradeVersion = "3.4";
+
+    // When the featureCompatibilityVersion is equal to the upgrade version, running isMaster with
+    // internalClient returns minWireVersion=maxWireVersion.
+    assert.commandWorked(adminDB.runCommand({setFeatureCompatibilityVersion: upgradeVersion}));
+    let res = adminDB.runCommand(isMasterCommand);
+    assert.commandWorked(res);
+    assert.eq(res.minWireVersion, res.maxWireVersion, tojson(res));
+
+    // When the featureCompatibilityVersion is upgrading, running isMaster with internalClient
+    // returns minWireVersion=maxWireVersion.
+    assert.writeOK(adminDB.system.version.update(
+        {_id: "featureCompatibilityVersion"},
+        {$set: {version: downgradeVersion, targetVersion: upgradeVersion}}));
+    res = adminDB.runCommand(isMasterCommand);
+    assert.commandWorked(res);
+    assert.eq(res.minWireVersion, res.maxWireVersion, tojson(res));
+
+    // When the featureCompatibilityVersion is downgrading, running isMaster with internalClient
+    // returns minWireVersion=maxWireVersion.
+    assert.writeOK(adminDB.system.version.update(
+        {_id: "featureCompatibilityVersion"},
+        {$set: {version: downgradeVersion, targetVersion: downgradeVersion}}));
+    res = adminDB.runCommand(isMasterCommand);
+    assert.commandWorked(res);
+    assert.eq(res.minWireVersion, res.maxWireVersion, tojson(res));
+
+    // When the featureCompatibilityVersion is equal to the downgrade version, running isMaster with
+    // internalClient returns minWireVersion<maxWireVersion.
+    assert.commandWorked(adminDB.runCommand({setFeatureCompatibilityVersion: downgradeVersion}));
+    res = adminDB.runCommand(isMasterCommand);
+    assert.commandWorked(res);
+    assert.lt(res.minWireVersion, res.maxWireVersion, tojson(res));
+
+    // When the internalClient field is missing from the isMaster command, the response has
+    // minWireVersion<maxWireVersion, even if the featureCompatibilityVersion is equal to the
+    // upgrade version.
+    assert.commandWorked(adminDB.runCommand({setFeatureCompatibilityVersion: upgradeVersion}));
+    res = adminDB.runCommand({isMaster: 1});
+    assert.commandWorked(res);
+    assert.lt(res.minWireVersion, res.maxWireVersion, tojson(res));
+})();