add tests

packages/browser/src/lib/__tests__/fetch.test.ts

@@ -0,0 +1,24 @@
+import unfetch from 'unfetch'
+import { getGlobal } from '../get-global'
+import { fetch } from '../fetch'
+
+jest.mock('unfetch')
+const unfetchMock = jest.mocked(unfetch).mockResolvedValue({} as Response)
+
+jest.mock('../get-global')
+const getGlobalMock = jest.mocked(getGlobal)
+
+describe(fetch, () => {
+  it('should call native fetch if available', async () => {
+    const fetchSpy = jest.fn()
+    getGlobalMock.mockReturnValue({ fetch: fetchSpy } as any)
+    void fetch('http://foo.com')
+    expect(unfetchMock).not.toBeCalled()
+    expect(fetchSpy).toBeCalled()
+  })
+  it('should fall back to unfetch', async () => {
+    getGlobalMock.mockReturnValue(null)
+    void fetch('http://foo.com')
+    expect(unfetchMock).toBeCalled()
+  })
+})

packages/browser/src/lib/fetch.ts

@@ -6,10 +6,6 @@ import { getGlobal } from './get-global'
  */
 export const fetch: typeof unfetch = (...args) => {
   const global = getGlobal()
-  let fetch = unfetch
-
-  if (global && global.fetch) {
-    fetch = global.fetch
-  }
-  return fetch(...args)
+  const fn = (global && global.fetch) || unfetch
+  return fn(...args)
 }