test: add fetch util tests

Author: janniks

packages/common/tests/fetchUtil.test.ts

@@ -0,0 +1,22 @@
+import fetchMock from 'jest-fetch-mock';
+import { createApiKeyMiddleware, createFetchFn } from '../src';
+
+describe('fetch middleware', () => {
+  test('createApiKeyMiddleware adds x-api-key to headers', async () => {
+    const apiKey = 'MY_KEY';
+
+    const middleware = createApiKeyMiddleware({ apiKey });
+    expect(middleware.pre).not.toBeNull();
+
+    const fetchFn = createFetchFn(middleware);
+
+    fetchMock.mockOnce('*', { status: 200 });
+
+    await fetchFn('https://example.com');
+    expect(fetchMock.mock.calls[0][1]?.headers).toBe(undefined);
+
+    await fetchFn('https://api.stacks.co');
+    expect(fetchMock.mock.calls[1][1]?.headers).toBeDefined();
+    expect((fetchMock.mock.calls[1][1]?.headers as Headers)?.get('x-api-key')).toContain(apiKey);
+  });
+});