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diff --git a/dom/heapsnapshot/tests/unit/test_deduplicatePaths_01.js b/dom/heapsnapshot/tests/unit/test_deduplicatePaths_01.js
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+++ b/dom/heapsnapshot/tests/unit/test_deduplicatePaths_01.js
@@ -0,0 +1,113 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+"use strict";
+
+// Test the behavior of the deduplicatePaths utility function.
+
+function edge(from, to, name) {
+  return { from, to, name };
+}
+
+function run_test() {
+  const a = 1;
+  const b = 2;
+  const c = 3;
+  const d = 4;
+  const e = 5;
+  const f = 6;
+  const g = 7;
+
+  dumpn("Single long path");
+  assertDeduplicatedPaths({
+    target: g,
+    paths: [
+      [
+        pathEntry(a, "e1"),
+        pathEntry(b, "e2"),
+        pathEntry(c, "e3"),
+        pathEntry(d, "e4"),
+        pathEntry(e, "e5"),
+        pathEntry(f, "e6"),
+      ]
+    ],
+    expectedNodes: [a, b, c, d, e, f, g],
+    expectedEdges: [
+      edge(a, b, "e1"),
+      edge(b, c, "e2"),
+      edge(c, d, "e3"),
+      edge(d, e, "e4"),
+      edge(e, f, "e5"),
+      edge(f, g, "e6"),
+    ]
+  });
+
+  dumpn("Multiple edges from and to the same nodes");
+  assertDeduplicatedPaths({
+    target: a,
+    paths: [
+      [pathEntry(b, "x")],
+      [pathEntry(b, "y")],
+      [pathEntry(b, "z")],
+    ],
+    expectedNodes: [a, b],
+    expectedEdges: [
+      edge(b, a, "x"),
+      edge(b, a, "y"),
+      edge(b, a, "z"),
+    ]
+  });
+
+  dumpn("Multiple paths sharing some nodes and edges");
+  assertDeduplicatedPaths({
+    target: g,
+    paths: [
+      [
+        pathEntry(a, "a->b"),
+        pathEntry(b, "b->c"),
+        pathEntry(c, "foo"),
+      ],
+      [
+        pathEntry(a, "a->b"),
+        pathEntry(b, "b->d"),
+        pathEntry(d, "bar"),
+      ],
+      [
+        pathEntry(a, "a->b"),
+        pathEntry(b, "b->e"),
+        pathEntry(e, "baz"),
+      ],
+    ],
+    expectedNodes: [a, b, c, d, e, g],
+    expectedEdges: [
+      edge(a, b, "a->b"),
+      edge(b, c, "b->c"),
+      edge(b, d, "b->d"),
+      edge(b, e, "b->e"),
+      edge(c, g, "foo"),
+      edge(d, g, "bar"),
+      edge(e, g, "baz"),
+    ]
+  });
+
+  dumpn("Second shortest path contains target itself");
+  assertDeduplicatedPaths({
+    target: g,
+    paths: [
+      [
+        pathEntry(a, "a->b"),
+        pathEntry(b, "b->g"),
+      ],
+      [
+        pathEntry(a, "a->b"),
+        pathEntry(b, "b->g"),
+        pathEntry(g, "g->f"),
+        pathEntry(f, "f->g"),
+      ],
+    ],
+    expectedNodes: [a, b, g],
+    expectedEdges: [
+      edge(a, b, "a->b"),
+      edge(b, g, "b->g"),
+    ]
+  });
+}