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simple-mock

travis npm downloads

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

Install

For Node:

$ npm install simple-mock

For Browser:

$ bower install simple-mock

Mock

Not sure when to use a mock, stub, or spy? Just use simple.mock.

Examples:

var simple = require('simple-mock')

simple.mock(obj, 'example', 'value') // Replace with this value

simple.mock(obj, 'example') // Spy on underlying method *or* stub
simple.mock(obj, 'example').callFn(function () {}) // Stub
simple.mock(obj, 'example').callbackWith(null, 'etc') // Stub
simple.mock(obj, 'example').returnWith('etc') // Stub
simple.mock(obj, 'example').throwWith(new Error()) // Stub
simple.mock(obj, 'example').resolveWith('etc') // Stub
simple.mock(obj, 'example').rejectWith(new Error()) // Stub
simple.mock(obj, 'example').callOriginal() // Unstubbed call

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.arg, error) // First parameter of the last call
assert.equals(fn.lastCall.args[1], 'etc') // Second 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):

var fn = simple.stub().returnWith('etc')

var returned = fn()

assert.equals(returned, 'etc')

Or spy on a standalone function:

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

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

See examples for more common usage patterns.

API

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

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.restore()

Restores all current mocks.

simple.restore(obj, key)

Use this if you need to restore only a single mock value or function on an object.

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 the call
  • call.context the context (this) of the 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.)

spy.reset()

Resets all counts and properties to the original state.

stub.callFn(fn)

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

stub.callOriginal()

Configures this stub to call the original, unstubbed function, returning its return value. 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.callback(...) or stub.callbackAtIndex(cbArgumentIndex, ...)

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

stub.inThisContext(obj)

Configures the last configured function or callback to be called in this context, i.e. this will be obj.

stub.resolveWith(val)

Configures the stub to return a Promise (where available] resolving to this value. Same as stub.returnWith(Promise.resolve(val)). You can use a custom Promise-conforming library, i.e. simple.Promise = require('bluebird') or simple.Promise = $q.

stub.rejectWith(val)

Configures the stub to return a Promise (where available) rejecting with this error. Same as stub.returnWith(Promise.reject(val)). You can use a custom Promise-conforming library, i.e. simple.Promise = require('bluebird') or simple.Promise = $q.

stub.actions

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

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

Note: modifying this array directly is not supported, rather use stub.withActions(actions) if you need to add actions.

stub.withActions(actions) or stub.withActions()

Configures this stub to use the specified array of actions. See stub.actions above for the syntax of an action.

var fn = simple.stub()
         .returnWith('a')
         .withActions([{ returnValue: 'b' }, { returnValue: 'c' }])
         .returnWith('d')

var returned1 = fn()
var returned2 = fn()
var returned3 = fn()
var returned4 = fn()

assert.equal(fn.callCount, 4)
assert.equal(returned1, 'a')
assert.equal(returned2, 'b')
assert.equal(returned3, 'c')
assert.equal(returned4, 'd')

stub.loop

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

stub.withLoop() & stub.noLoop()

Configures the stub to enable/disable looping.

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. Keep it simple!