1 files changed, 14 insertions, 0 deletions
diff --git a/js/src/jit-test/tests/collections/Map-set-size.js b/js/src/jit-test/tests/collections/Map-set-size.js
new file mode 100644
index 0000000000..3c4a13c85e
--- /dev/null
+++ b/js/src/jit-test/tests/collections/Map-set-size.js
@@ -0,0 +1,14 @@
+// map.set(k, v) increments the map size iff map didn't already have an entry for k.
+
+var m = new Map();
+m.set('a', 0);
+assertEq(m.size, 1);
+m.set('a', 0);
+assertEq(m.size, 1);
+m.set('a', undefined);
+assertEq(m.size, 1);
+
+m.set('b', 2);
+assertEq(m.size, 2);
+m.set('a', 1);
+assertEq(m.size, 2);