Stubbing a class method with Sinon.js

Question

I am trying to stub a method using sinon.js but I get the following error:

Uncaught TypeError: Attempted to wrap undefined property sample_pressure as function

I also went to this question (Stubbing and/or mocking a class in sinon.js?) and copied and pasted the code but I get the same error.

Here is my code:

Sensor = (function() {   // A simple Sensor class    // Constructor   function Sensor(pressure) {     this.pressure = pressure;   }    Sensor.prototype.sample_pressure = function() {     return this.pressure;   };    return Sensor;  })();  // Doesn't work var stub_sens = sinon.stub(Sensor, "sample_pressure").returns(0);  // Doesn't work var stub_sens = sinon.stub(Sensor, "sample_pressure", function() {return 0});  // Never gets this far console.log(stub_sens.sample_pressure()); 

Here is the jsFiddle (http://jsfiddle.net/pebreo/wyg5f/5/) for the above code, and the jsFiddle for the SO question that I mentioned (http://jsfiddle.net/pebreo/9mK5d/1/).

I made sure to include sinon in the External Resources in jsFiddle and even jQuery 1.9. What am I doing wrong?

Answer 1

Your code is attempting to stub a function on Sensor, but you have defined the function on Sensor.prototype.

sinon.stub(Sensor, "sample_pressure", function() {return 0}) 

is essentially the same as this:

Sensor["sample_pressure"] = function() {return 0}; 

but it is smart enough to see that Sensor["sample_pressure"] doesn't exist.

So what you would want to do is something like these:

// Stub the prototype's function so that there is a spy on any new instance // of Sensor that is created. Kind of overkill. sinon.stub(Sensor.prototype, "sample_pressure").returns(0);  var sensor = new Sensor(); console.log(sensor.sample_pressure()); 

or

// Stub the function on a single instance of 'Sensor'. var sensor = new Sensor(); sinon.stub(sensor, "sample_pressure").returns(0);  console.log(sensor.sample_pressure()); 

or

// Create a whole fake instance of 'Sensor' with none of the class's logic. var sensor = sinon.createStubInstance(Sensor); console.log(sensor.sample_pressure()); 

Answer 2

The top answer is deprecated. You should now use:

sinon.stub(YourClass.prototype, 'myMethod').callsFake(() => {     return {} }) 

Or for static methods:

sinon.stub(YourClass, 'myStaticMethod').callsFake(() => {     return {} }) 

Or for simple cases just use returns:

sinon.stub(YourClass.prototype, 'myMethod').returns({})  sinon.stub(YourClass, 'myStaticMethod').returns({}) 

Or if you want to stub a method for an instance:

const yourClassInstance = new YourClass(); sinon.stub(yourClassInstance, 'myMethod').returns({})