Replace fetch-mock with msw in tests

Use mock service worker (`msw`) in tests to more closely replicate a real
environment, mocking at the network level instead of at the API level.

This gives greater visibility into tests that are not properly isolated,
avoids issues specific to `fetch` or whichever request library is being used,
and could also be used for e2e testing in future.

Another motivation behind the change is the fact that `fetch-mock` hasn't been
updated in about 2 years and uses a number of deprecated packages including
`querystring` which will no longer receive updates for vulnerabilities.

config_frontend/msw.js

@@ -0,0 +1,21 @@
+/*
+Copyright 2022 The Tekton Authors
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+ http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { rest } from 'msw';
+import { setupServer } from 'msw/node';
+
+const server = setupServer(
+ rest.get(/\/properties$/, (req, res, ctx) => res(ctx.json({})))
+);
+
+export { rest, server };

config_frontend/setupTests.js

@@ -1,5 +1,5 @@
 /*
-Copyright 2019-2021 The Tekton Authors
+Copyright 2019-2022 The Tekton Authors
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at
@@ -13,23 +13,32 @@ limitations under the License.
 
 import { setLogger } from 'react-query';
 import fetch from 'node-fetch';
-import fetchMock from 'fetch-mock';
 import { TextDecoder, TextEncoder } from 'util';
 
+import { server } from './msw';
+
 setLogger({
  log: console.log, // eslint-disable-line no-console
  warn: console.warn, // eslint-disable-line no-console
  error: () => {}
 });
 
+// Establish API mocking before all tests.
+beforeAll(() =>
+ server.listen({
+ onUnhandledRequest: 'bypass' // reduce noise in test logs, TODO: revisit
+ })
+);
+// Reset any request handlers that we may add during the tests,
+// so they don't affect other tests.
+afterEach(() => server.resetHandlers());
+// Clean up after the tests are finished.
+afterAll(() => server.close());
+
 if (!global.fetch) {
  global.fetch = fetch;
 }
 
-fetchMock.catch();
-fetchMock.config.overwriteRoutes = true;
-fetchMock.config.warnOnFallback = false;
-
 window.HTMLElement.prototype.scrollIntoView =
  function scrollIntoViewTestStub() {};
 window.TextDecoder = TextDecoder;