Add toReturnValues and toHaveReturnedValues

Author: rickhanlonii

docs/ExpectAPI.md

@@ -649,6 +649,22 @@ test('drinkEach drinks each drink', () => {
 });
 ```
 
+### `.toHaveReturned(value)`
+
+Also under the alias: `.toReturn(value)`
+
+If you have a mock function, you can use `.toHaveReturned` to test that the spy
+returned a value. For example, let's say you have mock `drink` that returns
+`true`. You can write:
+
+```js
+test('drinks returns true', () => {
+  const drink = jest.fn(() => true);
+  drink();
+  expect(drink).toHaveReturned(true);
+});
+```
+
 ### `.toBeCloseTo(number, numDigits)`
 
 Using exact equality with floating point numbers is a bad idea. Rounding means

packages/expect/src/__tests__/__snapshots__/spy_matchers.test.js.snap

@@ -1059,3 +1059,75 @@ exports[`toHaveBeenNthCalledWith works with trailing undefined arguments 1`] = `
 Expected mock function first call to have been called with:
   Did not expect argument 2 but it was called with <red>undefined</>."
 `;
+
+exports[`toHaveReturned .not passes when called 1`] = `
+"<dim>expect(</><red>jest.fn()</><dim>).toHaveReturned(</><green>expected</><dim>)</>
+
+Expected mock function to have returned:
+  <green>\\"Some Other Value\\"</>"
+`;
+
+exports[`toHaveReturned .not passes when called with no arguments 1`] = `
+"<dim>expect(</><red>jest.fn()</><dim>).toHaveReturned(</><green>expected</><dim>)</>
+
+Expected mock function to have returned:
+  <green>undefined</>"
+`;
+
+exports[`toHaveReturned passes when called 1`] = `
+"<dim>expect(</><red>jest.fn()</><dim>).not.toHaveReturned(</><green>expected</><dim>)</>
+
+Expected mock function not to have returned:
+  <green>\\"Return Value\\"</>"
+`;
+
+exports[`toHaveReturned passes with no arguments 1`] = `
+"<dim>expect(</><red>jest.fn()</><dim>).not.toHaveReturned(</><green>expected</><dim>)</>
+
+Expected mock function not to have returned:
+  <green>undefined</>"
+`;
+
+exports[`toHaveReturned works only on spies or jest.fn 1`] = `
+"<dim>expect(</><red>jest.fn()</><dim>)[.not].toHaveReturned(</><dim>)</>
+
+<red>jest.fn()</> value must be a mock function or spy.
+Received:
+  function: <red>[Function fn]</>"
+`;
+
+exports[`toReturn .not passes when called 1`] = `
+"<dim>expect(</><red>jest.fn()</><dim>).toReturn(</><green>expected</><dim>)</>
+
+Expected mock function to have returned:
+  <green>\\"Some Other Value\\"</>"
+`;
+
+exports[`toReturn .not passes when called with no arguments 1`] = `
+"<dim>expect(</><red>jest.fn()</><dim>).toReturn(</><green>expected</><dim>)</>
+
+Expected mock function to have returned:
+  <green>undefined</>"
+`;
+
+exports[`toReturn passes when called 1`] = `
+"<dim>expect(</><red>jest.fn()</><dim>).not.toReturn(</><green>expected</><dim>)</>
+
+Expected mock function not to have returned:
+  <green>\\"Return Value\\"</>"
+`;
+
+exports[`toReturn passes with no arguments 1`] = `
+"<dim>expect(</><red>jest.fn()</><dim>).not.toReturn(</><green>expected</><dim>)</>
+
+Expected mock function not to have returned:
+  <green>undefined</>"
+`;
+
+exports[`toReturn works only on spies or jest.fn 1`] = `
+"<dim>expect(</><red>jest.fn()</><dim>)[.not].toReturn(</><dim>)</>
+
+<red>jest.fn()</> value must be a mock function or spy.
+Received:
+  function: <red>[Function fn]</>"
+`;

packages/expect/src/__tests__/spy_matchers.test.js

@@ -342,3 +342,70 @@ const jestExpect = require('../');
     }
   });
 });
+
+['toReturn', 'toHaveReturned'].forEach(called => {
+  describe(`${called}`, () => {
+    test(`works only on spies or jest.fn`, () => {
+      const fn = function fn() {};
+
+      expect(() => jestExpect(fn)[called]()).toThrowErrorMatchingSnapshot();
+    });
+
+    test(`passes with no arguments`, () => {
+      const fn = jest.fn();
+      fn();
+      jestExpect(fn)[called]();
+      expect(() => jestExpect(fn).not[called]()).toThrowErrorMatchingSnapshot();
+    });
+
+    test(`.not passes when called with no arguments`, () => {
+      const fn = jest.fn(() => 'Return Value');
+
+      fn();
+      jestExpect(fn).not[called]();
+      expect(() => jestExpect(fn)[called]()).toThrowErrorMatchingSnapshot();
+    });
+
+    test(`passes when called`, () => {
+      const fn = jest.fn(() => 'Return Value');
+      fn();
+      jestExpect(fn)[called]('Return Value');
+      expect(() =>
+        jestExpect(fn).not[called]('Return Value'),
+      ).toThrowErrorMatchingSnapshot();
+    });
+
+    test(`.not passes when called`, () => {
+      const fn = jest.fn(() => 'Return Value');
+      fn();
+      jestExpect(fn).not[called]('Some Other Value');
+      expect(() =>
+        jestExpect(fn)[called]('Some Other Value'),
+      ).toThrowErrorMatchingSnapshot();
+    });
+
+    test(`passes with mutliple calls`, () => {
+      const fn = jest.fn(a => a * 2);
+
+      fn(1);
+      fn(2);
+      fn(3);
+
+      jestExpect(fn)[called](2);
+      jestExpect(fn)[called](4);
+      jestExpect(fn)[called](6);
+    });
+
+    test(`.not passes with multiple calls`, () => {
+      const fn = jest.fn(a => a * 2);
+
+      fn(1);
+      fn(2);
+      fn(3);
+
+      jestExpect(fn).not[called](1);
+      jestExpect(fn).not[called](3);
+      jestExpect(fn).not[called](5);
+    });
+  });
+});

packages/expect/src/spy_matchers.js

@@ -118,6 +118,38 @@ const createToBeCalledWithMatcher = matcherName => (
   return {message, pass};
 };
 
+const createToReturnValuesMatcher = matcherName => (
+  received: any,
+  expected: any,
+) => {
+  ensureMock(received, matcherName);
+
+  const receivedIsSpy = isSpy(received);
+  const type = receivedIsSpy ? 'spy' : 'mock function';
+  const receivedName = receivedIsSpy ? 'spy' : received.getMockName();
+
+  const calls = receivedIsSpy
+    ? received.returnValues.all().map(x => x.args)
+    : received.mock.returnValues;
+
+  const [match] = partition(calls, call => equals(expected, call));
+  const pass = match.length > 0;
+
+  const message = pass
+    ? () =>
+        matcherHint('.not' + matcherName, receivedName) +
+        '\n\n' +
+        `Expected ${type} not to have returned:\n` +
+        `  ${printExpected(expected)}`
+    : () =>
+        matcherHint(matcherName, receivedName) +
+        '\n\n' +
+        `Expected ${type} to have returned:\n` +
+        `  ${printExpected(expected)}`;
+
+  return {message, pass};
+};
+
 const createLastCalledWithMatcher = matcherName => (
   received: any,
   ...expected: any
@@ -206,6 +238,8 @@ const spyMatchers: MatchersObject = {
   toHaveBeenNthCalledWith: createNthCalledWithMatcher(
     '.toHaveBeenNthCalledWith',
   ),
+  toHaveReturned: createToReturnValuesMatcher('.toHaveReturned'),
+  toReturn: createToReturnValuesMatcher('.toReturn'),
 };
 
 const isSpy = spy => spy.calls && typeof spy.calls.count === 'function';