Improve FE integration spec error logging

- The testing library logs are SO noisy.
  Let's trim it down a bit...
- Now the mock server console logs
  if a route bombs out.

spec/frontend_integration/test_helpers/setup/setup_mock_server.js

@@ -7,6 +7,16 @@ beforeEach(() => {
 
   const server = createMockServer();
   server.logging = false;
+  server.pretender.handledRequest = (verb, path, { status, responseText }) => {
+    if (status >= 500) {
+      // eslint-disable-next-line no-console
+      console.log(`
+The mock server returned status ${status} with "${verb} ${path}":
+
+${JSON.stringify({ responseText }, null, 2)}
+`);
+    }
+  };
 
   global.mockServer = server;
 });

spec/frontend_integration/test_helpers/setup/setup_testing_library.js

 import { configure } from '@testing-library/dom';
 
-configure({ asyncUtilTimeout: 10000 });
+const CUSTOM_ERROR_TYPE = 'TestingLibraryError';
+
+configure({
+  asyncUtilTimeout: 10000,
+  // Overwrite default error message to reduce noise.
+  getElementError: (messageArg) => {
+    // Add to message because the `name` doesn't look like it's used (although it should).
+    const message = `${CUSTOM_ERROR_TYPE}:\n\n${messageArg}`;
+    const error = new Error(message);
+    error.name = CUSTOM_ERROR_TYPE;
+    return error;
+  },
+});