diff --git a/frontend_tests/node_tests/narrow_unread.js b/frontend_tests/node_tests/narrow_unread.js
index 394e7c0759..7d71d30245 100644
--- a/frontend_tests/node_tests/narrow_unread.js
+++ b/frontend_tests/node_tests/narrow_unread.js
@@ -192,7 +192,6 @@ run_test('get_unread_ids', () => {
     ];
     set_filter(terms);
 
-    blueslip.set_test_data('warn', 'Unknown emails: bob@example.com');
     unread_ids = candidate_ids();
     assert.deepEqual(unread_ids, []);
 
diff --git a/frontend_tests/node_tests/zblueslip.js b/frontend_tests/node_tests/zblueslip.js
index 098fb37e3c..ac02212ace 100644
--- a/frontend_tests/node_tests/zblueslip.js
+++ b/frontend_tests/node_tests/zblueslip.js
@@ -30,10 +30,6 @@ run_test('basics', () => {
         blueslip.error('world');
     }
 
-    // Let's add an error that we are expecting from the module.
-    // The function 'set_test_data' pushes the expected error message to the array
-    // of messages expected for that log type; here, 'error'.
-    blueslip.set_test_data('error', 'hello');
     // Since the error 'world' is not being expected, blueslip will
     // throw an error.
     assert.throws(throw_an_error);
@@ -66,9 +62,6 @@ run_test('basics', () => {
         blueslip.warn('world');
     }
 
-    // Populate one valid value, and test with an invalid value.
-    // This should throw an error, and we'll assert it was thrown by zblueslip.
-    blueslip.set_test_data('warn', 'hello');
     assert.throws(throw_a_warning);
     blueslip.clear_test_data();
 
diff --git a/frontend_tests/zjsunit/index.js b/frontend_tests/zjsunit/index.js
index 57c07c849f..bbde68bc37 100644
--- a/frontend_tests/zjsunit/index.js
+++ b/frontend_tests/zjsunit/index.js
@@ -116,6 +116,11 @@ try {
         set_global('i18n', stub_i18n);
         namespace.clear_zulip_refs();
         run_one_module(file);
+
+        if (global.blueslip && blueslip.clear_test_data) {
+            blueslip.clear_test_data();
+        }
+
         namespace.restore();
     });
 } catch (e) {
diff --git a/frontend_tests/zjsunit/zblueslip.js b/frontend_tests/zjsunit/zblueslip.js
index 36be2d012b..5a83c215fe 100644
--- a/frontend_tests/zjsunit/zblueslip.js
+++ b/frontend_tests/zjsunit/zblueslip.js
@@ -11,28 +11,41 @@ exports.make_zblueslip = function () {
         error: true,
         fatal: true,
     };
+    const names = Array.from(Object.keys(opts));
 
     // Store valid test data for options.
     lib.test_data = {};
     lib.test_logs = {};
-    Object.keys(opts).forEach(name => {
+    lib.seen_messages = {};
+
+    for (const name of names) {
         lib.test_data[name] = [];
         lib.test_logs[name] = [];
-    });
+        lib.seen_messages[name] = new Set();
+    }
+
     lib.set_test_data = (name, message) => {
         lib.test_data[name].push(message);
     };
-    lib.clear_test_data = (name) => {
-        if (!name) {
-            // Clear all data
-            Object.keys(opts).forEach(name => {
-                lib.test_data[name] = [];
-                lib.test_logs[name] = [];
-            });
-            return;
+
+    lib.check_seen_messages = () => {
+        for (const name of names) {
+            for (const message of lib.test_data[name]) {
+                if (!lib.seen_messages[name].has(message)) {
+                    throw Error('Never saw: ' + message);
+                }
+            }
+        }
+    };
+
+    lib.clear_test_data = () => {
+        lib.check_seen_messages();
+
+        for (const name of names) {
+            lib.test_data[name] = [];
+            lib.test_logs[name] = [];
+            lib.seen_messages[name].clear();
         }
-        lib.test_data[name] = [];
-        lib.test_logs[name] = [];
     };
 
     lib.get_test_logs = (name) => {
@@ -40,13 +53,14 @@ exports.make_zblueslip = function () {
     };
 
     // Create logging functions
-    Object.keys(opts).forEach(name => {
+    for (const name of names) {
         if (!opts[name]) {
             // should just log the message.
             lib[name] = function (message, more_info, stack) {
+                lib.seen_messages[name].add(message);
                 lib.test_logs[name].push({message, more_info, stack});
             };
-            return;
+            continue;
         }
         lib[name] = function (message, more_info, stack) {
             if (typeof message !== 'string') {
@@ -58,6 +72,7 @@ exports.make_zblueslip = function () {
                     throw Error('message should be string: ' + message);
                 }
             }
+            lib.seen_messages[name].add(message);
             lib.test_logs[name].push({message, more_info, stack});
             const exact_match_fail = !lib.test_data[name].includes(message);
             if (exact_match_fail) {
@@ -66,7 +81,7 @@ exports.make_zblueslip = function () {
                 throw error;
             }
         };
-    });
+    }
 
     lib.exception_msg = function (ex) {
         return ex.message;