mi6

A library for making spies.

Example

var Mi6 = require('mi6');
var spy = Mi6();

spy.returns(25)
// or
spy.calls(function() {
  return 25;
});

var spy = Mi6(someFn);
spy.callsThrough();

spy(25);

expect(spy.calledWith(25)).to.be(true);
expect(spy.calledWith()).to.be(25);
expect(spy.called()).to.be(true);

spy();
expect(spy.calledWith()).to.be(undefined);

spy(1, 2, 3);
expect(spy.calledWith()).to.eql([1, 2, 3]);
expect(spy.calledWith(1, 2, 3)).to.be.ok();
expect(spy.callCount()).to.be(2);

Building Spies

Mi6 exposes helpers to overwrite methods on objects, and later restore them.

var Obj = {
  fn: function() { }
};
var Mi6 = require('mi6');

var spy = Mi6(Obj, 'fn');

spy.returns(5);
Obj.fn(); // returns 5;

Obj.fn.restore() // Restores fn to original fn

If a spy was created this way, you may later restore the original function on the object by calling spy.restore().

Working with Spies

Configuring Behavior

#calls(fn)

Makes a spy call fn.

var Spy = require('mi6').Spy;
var spy = new Spy();
var called = false;
spy.calls(function() { 
  called = true;
  return 2
});
spy(); // returns 2, called == true;

#callsThrough()

Makes a spy call the function it was initiantiated with.

var original = function() {
  return 5;
};
var spy = new Spy(original);
spy.callsThrough();
spy() == 5; // true

#returns(val)

Has a spy return a value rather than call a function.

var spy = new Spy();
spy.returns(5);
spy() == 5; // true

Testing Methods

#called()

Returns true if spy has been called, otherwise returns false.

var spy = new Spy();
spy();
expect(spy.called()).to.be(true);

#callCount()

Returns num where num is the number of times spy has been called.

var spy = new Spy();
spy();
spy();
spy();
expect(spy.callCount()).to.be(3);

#calledWith(...args)

If ...args is not specified, returns an array of what the spy was called with.

If ...args is specified, returns true if the spy was called with those arguments, otherwise it returns false.

var spy = new Spy();
spy(1);
expect(spy.calledWith()).to.eql([1]);
spy(2, 3);
expect(spy.calledWith(2, 3)).to.be(true);

Manipulation methods

#reset()

Resets the states of the spy for things like called, callCount and calledWith.

var spy = new Spy();
spy(1);
spy.reset();
expect(spy.called()).to.be(false);
expect(spy.calledWith()).to.be(undefined);