@aryzing/bun-mock-fetch

@aryzing/bun-mock-fetch

Mock fetch requests in Bun. Particularly useful when running tests.

bun add @aryzing/bun-mock-fetch

Basic usage:

mockFetch(requestMatcher, optionalMockResponseOptions);

Request matcher examples:

// Simple string matching
mockFetch("https://example.com");

// Using minimatch
mockFetch("https://example.com/foo/**");

// Using regex
mockFetch(/.*example.*/);

// Using a function
mockFetch((input, init) => input.url === "https://example.com");

// Using a detailed matcher object. All properties are optional.
mockFetch({
  // Must match this string, glob, or regex
  url: "https://example.com",
  // Must match this method (case-insensitive).
  method: "POST",
  // Must include these headers (case-insensitive) and match their values.
  headers: {
    "Content-Type": "application/json",
  },
});

Response options example:

mockFetch(/.*example.*/, {
  // The expected resolved value of Response.json() or Response.text().
  data: "Hello, world!",
  status: 200,
  headers: {
    "Content-Type": "text/plain",
  },
});

Example in tests,

afterEach(() => {
  clearFetchMocks();
});

test("first test", async () => {
  mockFetch("https://api.example.com", {
    response: {
      data: "first",
    },
  });
  expect(await makeApiRequest()).toBe("first");
});

test("second test", async () => {
  mockFetch("https://api.example.com", {
    response: {
      data: "second",
    },
  });
  expect(await makeApiRequest()).toBe("second");
});

Each call to mockFetch defines a new mock. At most one mock is used,, with each mock taking precendece over previously defined mocks.

By default, requests that aren't matched against any mock definitions are forwarded to the native built-in fetch. This behavior can be modified using setIsUsingBuiltInFetchFallback().

To clear the mocks and restore original built-in fetch,

clearFetchMocks();

Helpers

• setIsUsingBuiltInFetchFallback(value: boolean): Enable or disable using the built-in fetch for requests that haven't been matched against any mocks. Enabled by default.
• setIsVerbose(value: boolean): Enable or disable debugging logs. Disabled by default.