feat(test): warn developers when they re-use a test project name

[dhensche]

This warning would have saved me a fair bit of time during testing because test projects are not cleaned up between individual tests and I kept stepping on previous tests. If this is a dumb idea then you can just reject and ignore

[yyx990803]

Hmm this shouldn't be a problem because of the --force flag at line 42. Also yarn test runs yarn clean before starting the tests. Not sure how you run into the overwriting problem?

[dhensche]

As long as a clean is run between tests you're good, but if there are multiple tests in a spec that create test projects they reach need unique names to run the entire spec. Maybe I should restructure how I write tests to deal with this. An example of what I am talking about (or at least was running to when I was working on the feature) are the `should work` and `should not fix with --no-fix option` tests in https://github.com/vuejs/vue-cli/blob/dev/packages/%40vue/cli-plugin-typescript/__tests__/tsPluginTSLint.spec.js . Without having unique names, they kept stepping on each other during a test run because the `test` directory is not cleaned in between different tests in a spec

[yyx990803]

Ah ok, yeah it's common to forget changing the test project name after copy pasting when writing tests.