1 files changed, 107 insertions, 0 deletions
diff --git a/devtools/client/inspector/changes/test/browser_changes_declaration_duplicate.js b/devtools/client/inspector/changes/test/browser_changes_declaration_duplicate.js
new file mode 100644
index 0000000000..1d3423992e
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+++ b/devtools/client/inspector/changes/test/browser_changes_declaration_duplicate.js
@@ -0,0 +1,107 @@
+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that adding duplicate declarations to the Rule view is shown in the Changes panel.
+
+const TEST_URI = `
+  <style type='text/css'>
+    div {
+    }
+  </style>
+  <div></div>
+`;
+
+add_task(async function () {
+  await addTab("data:text/html;charset=utf-8," + encodeURIComponent(TEST_URI));
+  const { inspector, view: ruleView } = await openRuleView();
+  const { document: doc, store } = selectChangesView(inspector);
+
+  await selectNode("div", inspector);
+  await testAddDuplicateDeclarations(ruleView, store, doc);
+  await testChangeDuplicateDeclarations(ruleView, store, doc);
+  await testRemoveDuplicateDeclarations(ruleView, store, doc);
+});
+
+async function testAddDuplicateDeclarations(ruleView, store, doc) {
+  info(`Test that adding declarations with the same property name and value
+        are both tracked.`);
+
+  let onTrackChange = waitForDispatch(store, "TRACK_CHANGE");
+  info("Add CSS declaration");
+  await addProperty(ruleView, 1, "color", "red");
+  info("Wait for the change to be tracked");
+  await onTrackChange;
+
+  onTrackChange = waitForDispatch(store, "TRACK_CHANGE");
+  info("Add duplicate CSS declaration");
+  await addProperty(ruleView, 1, "color", "red");
+  info("Wait for the change to be tracked");
+  await onTrackChange;
+
+  await waitFor(() => {
+    const decls = getAddedDeclarations(doc);
+    return decls.length == 2 && decls[1].value == "red";
+  }, "Two declarations were tracked as added");
+  const addDecl = getAddedDeclarations(doc);
+  is(addDecl[0].value, "red", "First declaration has correct property value");
+  is(
+    addDecl[0].value,
+    addDecl[1].value,
+    "First and second declarations have identical property values"
+  );
+}
+
+async function testChangeDuplicateDeclarations(ruleView, store, doc) {
+  info(
+    "Test that changing one of the duplicate declarations won't change the other"
+  );
+  const prop = getTextProperty(ruleView, 1, { color: "red" });
+
+  info("Change the value of the first of the duplicate declarations");
+  const onTrackChange = waitForDispatch(store, "TRACK_CHANGE");
+  await setProperty(ruleView, prop, "black");
+  info("Wait for the change to be tracked");
+  await onTrackChange;
+
+  await waitFor(
+    () => getAddedDeclarations(doc).length == 2,
+    "Two declarations were tracked as added"
+  );
+  const addDecl = getAddedDeclarations(doc);
+  is(addDecl[0].value, "black", "First declaration has changed property value");
+  is(
+    addDecl[1].value,
+    "red",
+    "Second declaration has not changed property value"
+  );
+}
+
+async function testRemoveDuplicateDeclarations(ruleView, store, doc) {
+  info(`Test that removing the first of the duplicate declarations
+        will not remove the second.`);
+
+  const prop = getTextProperty(ruleView, 1, { color: "black" });
+
+  info("Remove first declaration");
+  const onTrackChange = waitForDispatch(store, "TRACK_CHANGE");
+  await removeProperty(ruleView, prop);
+  info("Wait for the change to be tracked");
+  await onTrackChange;
+
+  await waitFor(
+    () => getAddedDeclarations(doc).length == 1,
+    "One declaration was tracked as added"
+  );
+  const addDecl = getAddedDeclarations(doc);
+  const removeDecl = getRemovedDeclarations(doc);
+  // Expect no remove operation tracked because it cancels out the original add operation.
+  is(removeDecl.length, 0, "No declaration was tracked as removed");
+  is(addDecl.length, 1, "Just one declaration left tracked as added");
+  is(
+    addDecl[0].value,
+    "red",
+    "Leftover declaration has property value of the former second declaration"
+  );
+}