Generic/DisallowShortOpenTag: improve code coverage

[rodrigoprimo]

Description

This PR improves code coverage for the Generic.PHP.DisallowShortOpenTag sniff.

Related issues/external references

Part of #146

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
  • This change is only breaking for integrators, not for external standards or end-users.
• Documentation improvement

PR checklist

• I have checked there is no other PR open for the same change.
• I have read the Contribution Guidelines.
• I grant the project the right to include and distribute the code under the BSD-3-Clause license (and I have the right to grant these rights).
• I have added tests to cover my changes.
• I have verified that the code complies with the projects coding standards.
• [Required for new sniffs] I have added XML documentation for the sniff.

[rodrigoprimo]

@jrfnl, while checking your suggestion for the snippet clipping test (#638 (comment)), I noticed that the test to ensure that close tags are recognized as such only if placed after the open tag needs to be the last test on the file, as there should be no close tag after the open tag:

PHP_CodeSniffer/src/Standards/Generic/Tests/PHP/DisallowShortOpenTagUnitTest.3.inc

Lines 18 to 19 in 856fa77

	// Only recognize closing tag after opener.
	Some?> content <?

I wonder if we should indicate that in the code comment above it or if this test should be moved to its own file?

[jrfnl]

I wonder if we should indicate that in the code comment above it or if this test should be moved to its own file?

Adding a code comment would be good. As it's not a parse error, I don't think this needs a separate test file.

[rodrigoprimo]

Ok, I just added a comment documenting that the test must be the last one in the file.

[jrfnl]