diff --git a/internal/common/json_marshal_test.bzl b/internal/common/json_marshal_test.bzl
new file mode 100644
index 0000000..6c4b475
--- /dev/null
+++ b/internal/common/json_marshal_test.bzl
@@ -0,0 +1,33 @@
+"""Unit tests for json marshaling.
+
+Note, this cannot live next to the file it tests, because that file is in
+third_party bazel rules, and bazel doesn't support skylark testing yet.
+"""
+
+load("//third_party/bazel_skylib/lib:unittest.bzl", "asserts", "unittest")
+load("//third_party/bazel_rules/rules_typescript/internal:common/json_marshal.bzl", "json_marshal")
+
+def _test_impl(ctx):
+    env = unittest.begin(ctx)
+    asserts.equals(env, "\"abc\"", json_marshal("abc"))
+    asserts.equals(env, "123", json_marshal(123))
+    asserts.equals(env, "true", json_marshal(True))
+    asserts.equals(env, "false", json_marshal(False))
+    asserts.equals(env, "\"//a:b\"", json_marshal(Label("//a:b")))
+    asserts.equals(env, "[]", json_marshal([]))
+    asserts.equals(env, "{}", json_marshal({}))
+    asserts.equals(env, """[1, 2, 3]""", json_marshal([1, 2, 3]))
+    asserts.equals(env, """{"a": "b"}""", json_marshal({"a": "b"}))
+    asserts.equals(env, """{"none": false}""", json_marshal({"none": None}))
+    asserts.equals(
+        env,
+        """{"a": {"d": 1, "e": true, "f": ["f1", "f2"]}, "b": "val", "c": [{"g": false}]}""",
+        json_marshal({"a": {"d": 1, "e": True, "f": ["f1", "f2"]}, "b": "val", "c": [{"g": False}]}),
+    )
+
+    return unittest.end(env)
+
+_test = unittest.make(_test_impl)
+
+def json_marshal_test_suite():
+    unittest.suite("json_marshal_tests", _test)