tests: add E2E tests

[shvlv]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Tests.

What is the current behavior? (You can also link to an open issue here)
No E2E tests.

What is the new behavior (if this is a feature change)?
E2E tests to prevent possible regressions for Inpsyde and InpsydeTemplates CS usage.
See - #85.

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
No.

Other information:

[gmazzap]

Firts of all, thank you for this.

I'm not super-happy about the folders structure, I think it is not inline with current code.

The test-pakage is a fixture, after all. So it can go in the tests/fixture folder.

And the E2eTest.php file is a test case, so it can go in the tests/cases folder.

So we would have:

|_ tests/
    |_ cases/
        |_ e2e/
            |_ E2eTest.php
        |_ unit/
             |_ Helpers/
             FixturesTest.php
    |_ fixtures/
        |_ unit/
            |_ argument-type-declaration.php
            |_ disable-call-user-func.php
            |_ ...
        |_ e2e/
            |_ test-package/
    |_ src/
    |_ autoload.php
    |_ bootstrap.php

This requires a bit of adjustment for the paths uses right now, but I think it looks to me a better organization.

Alternatively:

|_ tests/
    |_ unit/
        cases/
            |_ Helpers/
             FixturesTest.php
        fixtures/
            |_ argument-type-declaration.php
            |_ disable-call-user-func.php
            |_ ...
    |_ e2e/
        |_ cases/
            |_ E2eTest.php
        |_ fixtures/
            |_ test-package/
    |_ src/
    |_ autoload.php
    |_ bootstrap.php

What do you think?

[shvlv]

I like the second approach more. Does it look good to you?