1 files changed, 39 insertions, 0 deletions
diff --git a/devtools/client/webconsole/test/browser/browser_webconsole_cached_messages_no_duplicate.js b/devtools/client/webconsole/test/browser/browser_webconsole_cached_messages_no_duplicate.js
new file mode 100644
index 0000000000..b7f8ee431b
--- /dev/null
+++ b/devtools/client/webconsole/test/browser/browser_webconsole_cached_messages_no_duplicate.js
@@ -0,0 +1,39 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Test to see if we don't get duplicated messages (cached and "live").
+// See Bug 1578138 for more information.
+
+"use strict";
+
+// Log 1 message every 50ms, until we reach 50 messages.
+const TEST_URI = `data:text/html,<!DOCTYPE html><meta charset=utf8><script>
+    var i = 0;
+    var intervalId = setInterval(() => {
+      if (i >= 50) {
+        clearInterval(intervalId);
+        intervalId = null;
+        return;
+      }
+      console.log("startup message " + (++i));
+    }, 50);
+  </script>`;
+
+add_task(async function () {
+  info("Add a tab and open the console");
+  const tab = await addTab(TEST_URI, { waitForLoad: false });
+  const hud = await openConsole(tab);
+
+  info("wait until all the messages are displayed");
+  await waitFor(
+    () =>
+      findConsoleAPIMessage(hud, "message 1") &&
+      findConsoleAPIMessage(hud, "message 50")
+  );
+
+  is(
+    (await findAllMessagesVirtualized(hud)).length,
+    50,
+    "We have the expected number of messages"
+  );
+});