thoroc•2d ago

Stubbing @std/x

I need some help understanding how to use the stub() method with @std/x libraries.

import * as stdYaml from 'jsr:@std/yaml';

 using _parse = stub(
    stdYaml,
    'parse',
    returnsNext([{ version: '3.8' }]),
  );

import * as stdYaml from 'jsr:@std/yaml';

 using _parse = stub(
    stdYaml,
    'parse',
    returnsNext([{ version: '3.8' }]),
  );

The code above seems to satisfy the linter, but the test obviously fails with the following:

sh 
error: MockError: Cannot stub: non-configurable instance method
    throw new MockError("Cannot stub: non-configurable instance method");

sh 
error: MockError: Cannot stub: non-configurable instance method
    throw new MockError("Cannot stub: non-configurable instance method");

3 Replies

Leokuma•2d ago

What you're trying to do is to mock a module's function, which is not supported. Try this workaround:

import * as stdYaml from 'jsr:@std/yaml';

 using _parse = stub(
    {parse: stdYaml.parse},
    'parse',
    returnsNext([{ version: '3.8' }]),
  );

import * as stdYaml from 'jsr:@std/yaml';

 using _parse = stub(
    {parse: stdYaml.parse},
    'parse',
    returnsNext([{ version: '3.8' }]),
  );

thorocOP•15h ago

That works like a charm. Shame about the lack of support natively, but at least I am unblocked. I think I might look into using external lib as I am not finding unit testing very easy using the @std libs

Leokuma•13h ago

If the difficulties you're facing are related to mocking, stubbing and spying, feel free to open an issue at https://github.com/denoland/std/issues. Reporting your difficulties could be helpful to others

Stubbing @std/x

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