1 files changed, 74 insertions, 0 deletions
diff --git a/dom/heapsnapshot/tests/unit/test_census_diff_01.js b/dom/heapsnapshot/tests/unit/test_census_diff_01.js
new file mode 100644
index 000000000..75977bccb
--- /dev/null
+++ b/dom/heapsnapshot/tests/unit/test_census_diff_01.js
@@ -0,0 +1,74 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Test diffing census reports of breakdown by "internalType".
+
+const BREAKDOWN = {
+  by: "internalType",
+  then: { by: "count", count: true, bytes: true }
+};
+
+const REPORT1 = {
+  "JSObject": {
+    "count": 10,
+    "bytes": 100,
+  },
+  "js::Shape": {
+    "count": 50,
+    "bytes": 500,
+  },
+  "JSString": {
+    "count": 0,
+    "bytes": 0,
+  },
+  "js::LazyScript": {
+    "count": 1,
+    "bytes": 10,
+  },
+};
+
+const REPORT2 = {
+  "JSObject": {
+    "count": 11,
+    "bytes": 110,
+  },
+  "js::Shape": {
+    "count": 51,
+    "bytes": 510,
+  },
+  "JSString": {
+    "count": 1,
+    "bytes": 1,
+  },
+  "js::BaseShape": {
+    "count": 1,
+    "bytes": 42,
+  },
+};
+
+const EXPECTED = {
+  "JSObject": {
+    "count": 1,
+    "bytes": 10,
+  },
+  "js::Shape": {
+    "count": 1,
+    "bytes": 10,
+  },
+  "JSString": {
+    "count": 1,
+    "bytes": 1,
+  },
+  "js::LazyScript": {
+    "count": -1,
+    "bytes": -10,
+  },
+  "js::BaseShape": {
+    "count": 1,
+    "bytes": 42,
+  },
+};
+
+function run_test() {
+  assertDiff(BREAKDOWN, REPORT1, REPORT2, EXPECTED);
+}