support buffers when mocking responses

tests/test.js

@@ -1,3 +1,4 @@
+const { StringDecoder } = require('string_decoder');
 const { APIRequest, APIRequest2, defaultRequestUri, request } = require('./api')
 
 describe('testing mockResponse and alias once', () => {
@@ -358,6 +359,15 @@ describe('request', () => {
       fetch('https://bar', {}).then((response) => response.headers.get('ding'))
     ).resolves.toEqual('dang')
   })
+
+  it('resolves with mocked response containing buffer', () => {
+    fetch.mockResponseOnce(() => Promise.resolve(new Response(Buffer.from('foo'))))
+    return expect(
+      fetch('https://bar', {})
+        .then((response) => response.arrayBuffer())
+        .then((arrayBuffer) => new StringDecoder('utf8').write(new Uint8Array(arrayBuffer)))
+    ).resolves.toEqual('foo')
+  });
 })
 
 describe('conditional mocking', () => {

types/index.d.ts

@@ -98,7 +98,7 @@ export interface MockResponseInit extends MockParams {
 export type ErrorOrFunction = Error | ((...args: any[]) => Promise<any>);
 export type UrlOrPredicate = string | RegExp | ((input: Request) => boolean);
 
-export type MockResponseInitFunction = (request: Request) => MockResponseInit | string | Promise<MockResponseInit | string>;
+export type MockResponseInitFunction = (request: Request) => MockResponseInit | string | Promise<MockResponseInit | string | Response>;
 
 // alias of fetchMock.enableMocks() for ES6 import syntax to not clash with other libraries
 export function enableFetchMocks(): void;

types/test.ts

@@ -10,6 +10,7 @@ fetchMock.mockResponse(JSON.stringify({foo: "bar"}), {
 fetchMock.mockResponse(JSON.stringify({foo: "bar"}), {});
 fetchMock.mockResponse(someAsyncHandler);
 fetchMock.mockResponse(someAsyncStringHandler);
+fetchMock.mockResponse(someAsyncBufferHandler)
 
 fetchMock.mockResponseOnce(JSON.stringify({foo: "bar"}));
 fetchMock.mockResponseOnce(JSON.stringify({foo: "bar"}), {
@@ -21,6 +22,7 @@ fetchMock.mockResponseOnce(JSON.stringify({foo: "bar"}), {
 fetchMock.mockResponseOnce(JSON.stringify({foo: "bar"}), {});
 fetchMock.mockResponseOnce(someAsyncHandler);
 fetchMock.mockResponseOnce(someAsyncStringHandler);
+fetchMock.mockResponseOnce(someAsyncBufferHandler)
 
 fetchMock.once(JSON.stringify({foo: "bar"}));
 fetchMock.once(JSON.stringify({foo: "bar"}), {
@@ -43,6 +45,7 @@ fetchMock.mockResponses(
     someAsyncHandler,
     someSyncStringHandler,
     someAsyncStringHandler,
+    someAsyncBufferHandler,
     [JSON.stringify({foo: "bar"}), {status: 200}]
 );
 
@@ -105,6 +108,10 @@ function someSyncStringHandler(): string {
     return JSON.stringify({foo: "bar"});
 }
 
+async function someAsyncBufferHandler(): Promise<Response> {
+    return new Response(Buffer.from('foo'));
+}
+
 enableFetchMocks();
 disableFetchMocks();
 fm.enableMocks();