Improves error message for toHaveBeenCalledWith

modules/Expectation.js

@@ -2,6 +2,7 @@ import isEqual from 'is-equal'
 import isRegExp from 'is-regex'
 import tmatch from 'tmatch'
 import has from 'has'
+import inspect from 'object-inspect'
 import assert from './assert'
 import { isSpy } from './SpyUtils'
 import {
@@ -473,8 +474,21 @@ class Expectation {
     )
 
     assert(
-      spy.calls.some(call => isEqual(call.arguments, expectedArgs)),
-      'spy was never called with %s',
+      spy.calls.length > 0,
+      ('spy was not called')
+    )
+    const genMessage = () => {
+      const actualArguments = spy.calls
+        .map(call => `- ${inspect(call.arguments)}`)
+        .join('\n')
+
+      return `spy was not called with:\n%s.\n\nIt was called with:\n ${actualArguments}`
+    }
+    const hasBeenCalled = spy.calls.some(call => isEqual(call.arguments, expectedArgs))
+
+    assert(
+      hasBeenCalled,
+      hasBeenCalled ? null : genMessage(),
       expectedArgs
     )
 

modules/__tests__/spyOn-test.js

@@ -36,6 +36,22 @@ describe('A function that was spied on', () => {
     spy.restore()
     expect(video.play).toNotEqual(spy)
   })
+
+  it('was called with the correct args', () => {
+    spy.restore()
+    video.play('some', 'args')
+    try {
+      expect(spy).toHaveBeenCalledWith('foo', 'bar')
+    } catch (err) {
+      const expected =
+        `|spy was not called with:
+         |[ \'foo\', \'bar\' ].
+         |
+         |It was called with:
+         | - [ \'some\', \'args\' ]`.replace(/^ *\|/gm, '')
+      expect(err.message).toEqual(expected)
+    }
+  })
 })
 
 describe('A function that was spied on but not called', () => {