diff --git a/frontend_tests/node_tests/message_store.js b/frontend_tests/node_tests/message_store.js
index 819f8b1aa6..288a09ba3a 100644
--- a/frontend_tests/node_tests/message_store.js
+++ b/frontend_tests/node_tests/message_store.js
@@ -87,7 +87,14 @@ function convert_recipients(people) {
     }));
 }
 
-run_test("add_message_metadata", () => {
+function test(label, f) {
+    run_test(label, (override) => {
+        message_store.clear_for_testing();
+        f(override);
+    });
+}
+
+test("add_message_metadata", () => {
     let message = {
         sender_email: "me@example.com",
         sender_id: me.user_id,
@@ -155,7 +162,7 @@ run_test("add_message_metadata", () => {
     ]);
 });
 
-run_test("message_booleans_parity", () => {
+test("message_booleans_parity", () => {
     // We have two code paths that update/set message booleans.
     // This test asserts that both have identical behavior for the
     // flags common between them.
@@ -195,7 +202,7 @@ run_test("message_booleans_parity", () => {
     });
 });
 
-run_test("errors", () => {
+test("errors", () => {
     // Test a user that doesn't exist
     let message = {
         type: "private",
@@ -229,7 +236,7 @@ run_test("errors", () => {
     );
 });
 
-run_test("update_booleans", () => {
+test("update_booleans", () => {
     const message = {};
 
     // First, test fields that we do actually want to update.
@@ -266,7 +273,7 @@ run_test("update_booleans", () => {
     assert.equal(message.unread, true);
 });
 
-run_test("update_property", () => {
+test("update_property", () => {
     const message1 = {
         type: "stream",
         sender_full_name: alice.full_name,
@@ -315,7 +322,7 @@ run_test("update_property", () => {
     assert.equal(message2.display_recipient, denmark.name);
 });
 
-run_test("message_id_change", () => {
+test("message_id_change", () => {
     const message = {
         sender_email: "me@example.com",
         sender_id: me.user_id,
@@ -353,7 +360,7 @@ run_test("message_id_change", () => {
     }
 });
 
-run_test("errors", () => {
+test("errors", () => {
     blueslip.expect("error", "message_store.get got bad value: undefined");
     message_store.get(undefined);
 });
diff --git a/static/js/message_store.js b/static/js/message_store.js
index b13932d69f..525218f45d 100644
--- a/static/js/message_store.js
+++ b/static/js/message_store.js
@@ -23,6 +23,11 @@ const stored_messages = new Map();
 */
 const message_user_ids = new Set();
 
+export function clear_for_testing() {
+    stored_messages.clear();
+    message_user_ids.clear();
+}
+
 export function user_ids() {
     return Array.from(message_user_ids);
 }