1 files changed, 55 insertions, 0 deletions
diff --git a/jstests/replsets/reconfig_may_not_remove_custom_wc_in_use.js b/jstests/replsets/reconfig_may_not_remove_custom_wc_in_use.js
new file mode 100644
index 00000000000..8ee1a7ced02
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+++ b/jstests/replsets/reconfig_may_not_remove_custom_wc_in_use.js
@@ -0,0 +1,55 @@
+/**
+ * Tests that we may not use reconfig to remove a custom write concern definition that
+ * is currently set to the default. We are free to remove that definition once it is no longer in
+ * use.
+ */
+
+(function() {
+"use strict";
+load("jstests/libs/write_concern_util.js");
+load("jstests/replsets/rslib.js");
+
+const name = jsTestName();
+const rst = new ReplSetTest({
+    name: name,
+    nodes: [
+        {rsConfig: {tags: {region: "us"}}},
+        {rsConfig: {tags: {region: "us"}}},
+        {rsConfig: {tags: {region: "eu"}}}
+    ],
+    settings: {getLastErrorModes: {multiRegion: {region: 2}}}
+});
+
+rst.startSet();
+rst.initiate();
+
+const primary = rst.getPrimary();
+
+jsTestLog("Setting the write concern to match the custom definition.");
+assert.commandWorked(
+    primary.adminCommand({setDefaultRWConcern: 1, defaultWriteConcern: {w: "multiRegion"}}));
+
+let cfg = rst.getReplSetConfigFromNode();
+cfg.settings.getLastErrorModes = {};
+
+jsTestLog("Attempting reconfig to remove the definition while it is still in use (should fail).");
+assert.throwsWithCode(() => {
+    reconfig(rst, cfg);
+}, ErrorCodes.NewReplicaSetConfigurationIncompatible);
+
+jsTestLog("Resetting the write concern to majority.");
+assert.commandWorked(primary.adminCommand({setDefaultRWConcern: 1, defaultWriteConcern: {w: 2}}));
+
+jsTestLog(
+    "Removing custom write concern definition now that it is no longer in use (should succceed).");
+cfg = rst.getReplSetConfigFromNode();
+cfg.settings.getLastErrorModes = {};
+reconfig(rst, cfg);
+
+jsTestLog("Checking writeability.");
+const coll = primary.getDB("db").getCollection("coll");
+assert.commandWorked(coll.insert({a: 1}));
+rst.awaitReplication();
+
+rst.stopSet();
+})();