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+# CredentialManagement Testing
+
+## OTPCredential Testing
+
+In this test suite `otpcredential-helper.js` is a testing framework that enables
+engines to test OTPCredential by intercepting the connection between the browser
+and the underlying operating system and mock its behavior.
+
+Usage:
+
+1. Include the following in your test:
+```html
+<script src="/resources/test-only-api.js"></script>
+<script src="support/otpcredential-helper.js"></script>
+```
+2. Set expectations
+```javascript
+await expect(receive).andReturn(() => {
+  // mock behavior
+})
+```
+3. Call `navigator.credentials.get({otp: {transport: ["sms"]}})`
+4. Verify results
+
+The mocking API is browser agnostic and is designed such that other engines
+could implement it too.
+
+Here are the symbols that are exposed to tests that need to be implemented
+per engine:
+
+- function receive(): the main/only function that can be mocked
+- function expect(): the main/only function that enables us to mock it
+- enum State {kSuccess, kTimeout}: allows you to mock success/failures
+
+## FedCM Testing
+
+`fedcm-mojojs-helper.js` exposes `fedcm_mojo_mock_test` which is a specialized
+`promise_test` which comes pre-setup with the appropriate mocking infrastructure
+to emulate platform federated auth backend. The mock is passed to the test
+function as the second parameter.
+
+Example usage:
+```
+<script type="module">
+  import {fedcm_mojo_mock_test} from './support/fedcm-mojojs-helper.js';
+
+  fedcm_mojo_mock_test(async (t, mock) => {
+    mock.returnToken("https://idp.test/fedcm.json", "a_token");
+    assert_equals("a_token", await navigator.credentials.get(options));
+  }, "Successfully obtaining a token using mock.");
+</script>
+```
+
+The chromium implementation uses the MojoJS shim.