feat: mock node-fetch's export pattern

Modified `FetchMock.sandbox`'s method to return an interface that more
closely mocks `node-fetch`'s export pattern.
Created tests to verify the new return value.

src/lib/index.js

@@ -55,11 +55,17 @@ FetchMock.sandbox = function() {
 	const sandbox = Object.assign(
 		proxy, // Ensures that the entire returned object is a callable function
 		FetchMock, // prototype methods
-		this.createInstance() // instance data
+		this.createInstance(), // instance data
+		{
+			Headers: this.config.Headers,
+			Request: this.config.Request,
+			Response: this.config.Response
+		}
 	);
 
 	sandbox.bindMethods();
 	sandbox.isSandbox = true;
+	sandbox.default = sandbox;
 	return sandbox;
 };
 

test/specs/sandbox.test.js

@@ -144,5 +144,20 @@ module.exports = (fetchMock, theGlobal) => {
 			fm.config.fetch = originalFetch;
 			expect(() => fm.spy()).not.to.throw();
 		});
+
+		it('exports a properly mocked node-fetch module shape', () => {
+			// uses node-fetch default require pattern
+			const {
+				default: fetch,
+				Headers,
+				Request,
+				Response
+			} = fetchMock.sandbox();
+
+			expect(fetch.name).to.equal('proxy');
+			expect(new Headers()).to.be.an.instanceOf(fetchMock.config.Headers);
+			expect(new Request()).to.be.an.instanceOf(fetchMock.config.Request);
+			expect(new Response()).to.be.an.instanceOf(fetchMock.config.Response);
+		});
 	});
 };