Any way to modify Jasmine spies based on arguments?

Question

I have a function I'd like to test which calls an external API method twice, using different parameters. I'd like to mock this external API out with a Jasmine spy, and return different things based on the parameters. Is there any way to do this in Jasmine? The best I can come up with is a hack using andCallFake:

var functionToTest = function() { var userName = externalApi.get('abc'); var userId = externalApi.get('123'); }; describe('my fn', function() { it('gets user name and ID', function() { spyOn(externalApi, 'get').andCallFake(function(myParam) { if (myParam == 'abc') { return 'Jane'; } else if (myParam == '123') { return 98765; } }); }); });

Why did you feel and.callFake was a hack? Looks like a good/best answer to me. — ruffin
– ruffin, Commented Jan 12, 2021 at 21:14

Jason McTaggart · Accepted Answer · 2018-07-26 19:41:40Z

In Jasmine versions 3.0 and above you can use withArgs

describe('my fn', function() { it('gets user name and ID', function() { spyOn(externalApi, 'get') .withArgs('abc').and.returnValue('Jane') .withArgs('123').and.returnValue(98765); }); });

For Jasmine versions earlier than 3.0 callFake is the right way to go, but you can simplify it using an object to hold the return values

describe('my fn', function() { var params = { 'abc': 'Jane', '123': 98765 } it('gets user name and ID', function() { spyOn(externalApi, 'get').and.callFake(function(myParam) { return params[myParam] }); }); });

Depending on the version of Jasmine, the syntax is slightly different:

1.3.1: .andCallFake(fn)
2.0: .and.callFake(fn)

Resources:

I had to return different promises, so the return looked slightly different: return q.when(params[myParam]);. Otherwise, this was a spot on solution to my problem. My dream solution would be to change "and.returnValue" calls.
feels like jasmine should have a better way of declaring this. Like spyOn(fake, 'method').withArgs('abc').and.returnValue('Jane') and spyOn(fake, 'method').withArgs('123').and.returnValue(98765).
@jrharshath .withArgs is not working for me in jasmine 2.0
.withArgs is not really available - I meant that such a method would make sense when writing tests.

akhouri · Accepted Answer · 2016-11-15 06:17:33Z

You could also use $provide to create a spy. And mock using and.returnValues instead of and.returnValue to pass in parameterised data.

As per Jasmine docs: By chaining the spy with and.returnValues, all calls to the function will return specific values in order until it reaches the end of the return values list, at which point it will return undefined for all subsequent calls.

describe('my fn', () => { beforeEach(module($provide => { $provide.value('externalApi', jasmine.createSpyObj('externalApi', ['get'])); })); it('get userName and Id', inject((externalApi) => { // Given externalApi.get.and.returnValues('abc','123'); // When //insert your condition // Then // insert the expectation })); });

This is the correct answer, since a test should always know exactly how a spy will be called, and therefore should just use returnValues to support multiple calls
Just to clarify akhouri's answer: this method only works when the externalApi.get.and.returnValues('abc','123') is called within the it function. Otherwise if you set a list of values, else where, it shall never work because the order in which tests are ran is not predictable. In fact tests should not depend on the order in which they are executed.

Guillermo · Accepted Answer · 2020-02-04 19:02:09Z

In my case, I had a component I was testing and, in its constructor, there is a config service with a method called getAppConfigValue that is called twice, each time with different arguments:

constructor(private configSvc: ConfigService) { this.configSvc.getAppConfigValue('a_string'); this.configSvc.getAppConfigValue('another_string'); }

In my spec, I provided the ConfigService in the TestBed like so:

{ provide: ConfigService, useValue: { getAppConfigValue: (key: any): any { if (key === 'a_string) { return 'a_value'; } else if (key === 'another_string') { return 'another_value'; } } } as ConfigService }

So, as long as the signature for getAppConfigValue is the same as specified in the actual ConfigService, what the function does internally can be modified.

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Any way to modify Jasmine spies based on arguments?

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