Tests: add @group Windows to more tests + mention in CONTRIBUTING

.github/CONTRIBUTING.md

@@ -339,6 +339,13 @@ Example:
 for
 ```
 
+#### Tests covering code which has OS-specific behaviour
+
+Most code in PHP_CodeSniffer is operating system agnostic.
+However, there are a few places which include OS-specific conditions, most notably for Windows.
+
+Tests which cover code which have Windows specific conditions should be marked with a `@group Windows` annotation to allow for running those tests separately/selectively in CI.
+
 
 ### Submitting Your Pull Request
 

.github/workflows/test.yml

@@ -92,6 +92,11 @@ jobs:
         php: ['5.4', '5.5', '5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4', '8.5']
         custom_ini: [false]
 
+        exclude:
+          # Installing on Windows with PHP 5.4 runs into all sorts of problems (which are not ours).
+          - php: '5.4'
+            os: 'windows-latest'
+
         include:
           # Skip test runs on builds which are also run in the coverage job.
           # Note: the tests on PHP 7.2 will still be run as the coverage build uses custom_ini settings for that version.

src/Standards/Generic/Tests/Debug/CSSLintUnitTest.php

@@ -16,6 +16,8 @@
  * Unit test class for the CSSLint sniff.
  *
  * @covers \PHP_CodeSniffer\Standards\Generic\Sniffs\Debug\CSSLintSniff
+ * @covers \PHP_CodeSniffer\Config::getExecutablePath
+ * @group  Windows
  */
 final class CSSLintUnitTest extends AbstractSniffUnitTest
 {

tests/Core/Fixer/GenerateDiffTest.php

@@ -21,6 +21,7 @@
  * test running the fixer itself, nor generating a diff based on a fixer run.
  *
  * @covers PHP_CodeSniffer\Fixer::generateDiff
+ * @group  Windows
  */
 final class GenerateDiffTest extends TestCase
 {