Append --allow-prereleases to black installation command when Poetry is used

[notpushkin]

Similar to #5393.

For #5756 (it has been mistakenly closed as a duplicate of #5171, but the latter was about Pipenv and the former is about Poetry :)

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Has a news entry file (remember to thank yourself!)
• Appropriate comments and documentation strings in the code
• Has sufficient logging.
• Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• Test plan is updated as appropriate
• package-lock.json has been regenerated by running npm install (if dependencies have changed)
• The wiki is updated with any design decisions/details.

[msftclas]

All CLA requirements met.

[notpushkin]

Could you take a look @DonJayamanne? :)

[kimadeline]

Hi @notpushkin , thank you for submitting this pull request! Could you add some tests for it? Rest looks good 👍

[kimadeline]

Add tests (see comment #5967 (comment))

[notpushkin]

Thanks for a review @kimadeline! I took a look at the existing tests and I see that tests for Poetry are in a separate file and do not iterate over the Product enum (like the tests for pip / pipenv / conda), so I'm not sure where I can plug the test for the changes I've made. Could you give me a hint? :-)

[kimadeline]

You were on the right track when you mentioned poetryInstaller.unit.test.ts. The last unit test of the suite on line 114 checks the content of the execution info array, so you could append a new test that asserts equality when the module name is black:

test('Get executable info when installing black', async () => {
        const uri = Uri.file(__dirname);
        const settings = mock(PythonSettings);

        when(configurationService.getSettings(uri)).thenReturn(instance(settings));
        when(settings.poetryPath).thenReturn('poetry path');

        const info = await poetryInstaller.getExecutionInfo('black', uri);

        assert.deepEqual(info, { args: ['add', '--dev', 'black', '--allow-prereleases'], execPath: 'poetry path' });
    });

[notpushkin]

Thank you so much @kimadeline! Added the test case and it works alright:

$ npm run test:unittests -- --grep='installing black'

> [email protected] test:unittests /home/ale/dev/vscode-python
> mocha --require source-map-support/register --opts ./build/.mocha.unittests.opts "--grep=installing black"

(node:1381) [DEP0016] DeprecationWarning: 'root' is deprecated, use 'global'
  Module Installer - Poetry
    ✓ Get executable info when installing black

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