getting `then is not a function` error while mocking http promise service

Question

Original service

getVersionDataValuesforPopup(Docversion, versionname, Structureweek, docVersionFieldID, versionid, WLTP) {
        return this.http.get(this.apiUrl + 'GetElementPopUpData?docVersion=' + Docversion + '&versionVariant=' + versionname
            + '&structureWeek=' + Structureweek + '&docVersionFieldID=' + docVersionFieldID
            + ' &VersionId=' + versionid + ' &isWLTP=' + WLTP, { withCredentials: true })
            .toPromise().then(responce => <CoCCreateVersionPopupPage[]>responce.json())
            .catch(error => {
                return error;
            });
    }

Calling original service in component

this.createversionservice.getVersionDataValuesforPopup(this.cocviewversiondatapage.docVersion,
            this.cocviewversiondatapage.VersionDescriptions,
            this.cocviewversiondatapage.structWeek, dataitems.DocumentVersionFieldId, this.cocviewversiondatapage.Id,
            this.cocviewversiondatapage.WLTP)
            .then(
            data=> { ...});

Mock service via constructor injection

getVersionDataValuesforPopup(Docversion, versionname, Structureweek, docVersionFieldID, versionid, WLTP) {
        return Observable.of({ Result: {} });
    }

I got an error while test the method

TypeError: this.createversionservice.getVersionDataValuesforPopup(...).then is not a function

I know the reason for the error, I am using Observable in my mock service but the real service has promise, So then callback does not support.Kindly let me know how can write a mock service for a http promise service call.

I will suggest some thing like this: return new Promise((resolve) => { resolve(null); }); — Nour
– Nour, Commented Feb 7, 2018 at 8:43
@Nour Yup. that is working for me. Could you please post this as an answer. i'll mark that a correct answer — Ramesh Rajendran
– Ramesh Rajendran, Commented Feb 7, 2018 at 9:50

JoWinchester · Accepted Answer · 2018-02-07 08:50:52Z

2

What testing framework are you using?

I would create a spy, for example with Jasmine:

spyOn(createversionservice, 'getVersionDataValuesforPopup')

you can then check that your function was called.

If you want to return a promise you can use the .andReturnValue() method, for example:

var promise = Promise.resolve('result');
spyOn(createversionservice, 'getVersionDataValuesforPopup').andReturnValue(promise);

Similar spys will exist in other frameworks

You can then check the method was called (or whatever test you want, for example:

expect(createversionservice.getVersionDataValuesforPopup).toHaveBeenCalled()

answered Feb 7, 2018 at 8:50

JoWinchester

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2 Comments

M Akin Over a year ago

I got this error because I didn't have that function name in my mock service

Anurag Prashant Over a year ago

Solves my problem.

Ramesh Rajendran · Accepted Answer · 2018-02-07 09:54:03Z

1

Would you please try the following:

return new Promise((resolve) => { resolve({}); });

edited Feb 7, 2018 at 9:54

Ramesh Rajendran

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answered Feb 7, 2018 at 9:53

Nour

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Comments

Srithar Rajendran · Accepted Answer · 2021-09-22 17:53:31Z

1

I have resolved using below code:

Promise.resolve({then: jest.fn()})

answered Sep 22, 2021 at 17:53

Srithar Rajendran

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1 Comment

Vishal Desai Over a year ago

This should be the correct answer. It also solves if you get the same error for .catch block. Promise.resolve({then: jest.fn(), catch: jest.fn()})

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