simple-mock

simple-mock

Super simple mocks, stubs, and spies with 1-step sandbox restore.

Install

npm install simple-mock

(For the browser, expose the index.js found at the top level of this repository.)

Mock

You can mock any function or value on an object and easily restore it.

Examples

simple.mock(obj, 'example', 'value'); // Replace with this value
simple.mock(obj, 'example', function() {}); // Replace with this function

simple.mock(obj, 'example') // Spy on underlying method *or* stub
simple.mock(obj, 'example').callbackWith(null, 'etc'); // Stub
simple.mock(obj, 'example').returnWith('etc'); // Stub
simple.mock(obj, 'example').throwWith(new Error()); // Stub

Then, to make sure all objects are back to the state the were in before your mocks:

simple.restore(); // Ideally called in an afterEach() block

callbackWith, returnWith and throwWith can be chained for queued behaviour, e.g.

simple.mock(Something.prototype, 'example')
  .callbackWith(null, 'etc')
  .callbackWith(new Error());

callbackWith, returnWith and throwWith configurations are stored on a simple array fn.actions

Expectations

You define your expectations with your own choice of assertion library.

assert(fn.called);
assert.equals(fn.callCount, 3);
assert.equals(fn.lastCall.args[0], error); // First parameter of the last call
assert.equals(fn.calls[0].returned, 'etc');
assert.equals(fn.calls[1].threw, error);

Standalone Stubs and Spies

If you need to create a standalone stub (stubs are also spies):

simple.stub().callbackWith(null, 'etc');
simple.stub().returnWith('etc');
simple.stub().throwWith(new Error());

Or spy on a standalone function:

var fn = simple.spy(function(){});

assert.equals(fn.callCount, 0);
assert.equals(fn.calls, []);

API

For var simple = require('simple-mock'):

simple.restore()

Restores all current mocks.

simple.mock(obj, key, value)

Sets the value on this object. E.g. mock(config, 'title', 'test') is the same as config.title = 'test', but restorable with all mocks.

simple.mock(obj, key, fn)

Wraps fn in a spy and sets this on the obj, restorable with all mocks.

simple.mock(obj, key)

If obj has already has this function, it is wrapped in a spy. The resulting spy can be turned into a stub by further configuration. Restores with all mocks.

simple.spy(fn) or simple.mock(fn)

Wraps fn in a spy.

simple.stub() or simple.mock()

Returns a stub function that is also a spy.

---

spy.called

Boolean

spy.callCount

Number of times the function was called.

spy.calls

An array of calls, each having these properties:

• call.args an array of arguments received on this call
• call.returned the value returned by the wrapped function
• call.threw the error thrown by the wrapped function
• call.k autoincrementing number, can be compared to evaluate call order

spy.lastCall

The last call object, with properties as above. (This is often also the first and only call.)

---

stub.callbackWith(...) or stub.callbackArgWith(argumentIndex, ...)

Configures this stub to call back with the arguments passed. It will use either the last argument as callback, or the argument at argumentIndex. Subsequent calls of this on the same stub (chainable) will queue up different behaviours for each subsequent call of the stub.

stub.returnWith(val)

Configures this stub to return with this value. Subsequent calls of this on the same stub (chainable) will queue up different behaviours for each subsequent call of the stub.

stub.throwWith(err)

Configures this stub to throw this error. Subsequent calls of this on the same stub (chainable) will queue up different behaviours for each subsequent call of the stub.

stub.actions

An array of behaviours, each having one of these properties:

• action.cbArgs arguments to call back with
• action.returnValue
• action.throwError

stub.loop

Boolean (default: true) setting whether the queue of actions for this stub should repeat.

Why

The most complete, framework-agnostic mocking library is sinon.js. It also has pages of documentation and lots of sugar-coating that we generally don't need. Just because it is there doesn't mean you need it. Keep it simple!