Build/Test Tools: Change the inheritance order of the abstract test classes.

As things were, the inheritance order of the abstract test classes was as follows:
{{{
WP_UnitTestCase (PHPUnit adapter layer)
    extends WP_UnitTestCase_Base (base test class)
        extends PHPUnit\Framework\TestCase (PHPUnit native class)
}}}

Concrete (child) test classes, as well as more specific abstract TestCases, are/were expected to extend the `WP_UnitTestCase`.

This order is not optimal as it means that the `WP_UnitTestCase_Base` class would not be able to benefit from any polyfills and/or shims in the PHPUnit adapter layer.

With that in mind, this commit changes the inheritance to:
{{{
WP_UnitTestCase (empty class, left in place to not break BC for plugin/theme integration tests)
    extends WP_UnitTestCase_Base (base test class)
        extends PHPUnit_Adapter_TestCase (PHPUnit adapter layer)
            extends PHPUnit\Framework\TestCase (PHPUnit native class)
}}}

The new order allows for the `WP_UnitTestCase_Base` to also benefit from the PHPUnit adapter layer.

For backward compatibility reasons the `WP_UnitTestCase`, which all test classes are (were) expected to extend, is left in place, though it is now an empty class and explicitly `abstract`.

Follow-up to [51559], [51560].

Props jrf, hellofromTonya, johnbillion, netweb, SergeyBiryukov.
See #46149.

git-svn-id: https://develop.svn.wordpress.org/trunk@51561 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/includes/abstract-testcase.php

@@ -12,7 +12,7 @@ require_once __DIR__ . '/trac.php';
  *
  * All WordPress unit tests should inherit from this class.
  */
-abstract class WP_UnitTestCase_Base extends PHPUnit\Framework\TestCase {
+abstract class WP_UnitTestCase_Base extends PHPUnit_Adapter_TestCase {
 
 	protected static $forced_tickets   = array();
 	protected $expected_deprecated     = array();

tests/phpunit/includes/bootstrap.php

@@ -207,6 +207,7 @@ if ( version_compare( tests_get_phpunit_version(), '6.0', '>=' ) ) {
 require_once $phpunit_polyfills_autoloader;
 unset( $phpunit_polyfills_autoloader );
 
+require __DIR__ . '/phpunit-adapter-testcase.php';
 require __DIR__ . '/abstract-testcase.php';
 require __DIR__ . '/testcase.php';
 require __DIR__ . '/testcase-rest-api.php';

tests/phpunit/includes/phpunit-adapter-testcase.php

@@ -0,0 +1,45 @@
+<?php
+
+use Yoast\PHPUnitPolyfills\Helpers\AssertAttributeHelper;
+use Yoast\PHPUnitPolyfills\Polyfills\AssertClosedResource;
+use Yoast\PHPUnitPolyfills\Polyfills\AssertEqualsSpecializations;
+use Yoast\PHPUnitPolyfills\Polyfills\AssertFileDirectory;
+use Yoast\PHPUnitPolyfills\Polyfills\AssertFileEqualsSpecializations;
+use Yoast\PHPUnitPolyfills\Polyfills\AssertionRenames;
+use Yoast\PHPUnitPolyfills\Polyfills\AssertIsType;
+use Yoast\PHPUnitPolyfills\Polyfills\AssertNumericType;
+use Yoast\PHPUnitPolyfills\Polyfills\AssertObjectEquals;
+use Yoast\PHPUnitPolyfills\Polyfills\AssertStringContains;
+use Yoast\PHPUnitPolyfills\Polyfills\EqualToSpecializations;
+use Yoast\PHPUnitPolyfills\Polyfills\ExpectException;
+use Yoast\PHPUnitPolyfills\Polyfills\ExpectExceptionMessageMatches;
+use Yoast\PHPUnitPolyfills\Polyfills\ExpectExceptionObject;
+use Yoast\PHPUnitPolyfills\Polyfills\ExpectPHPException;
+
+/**
+ * PHPUnit adapter layer.
+ *
+ * This class enhances the PHPUnit native `TestCase` with polyfills
+ * for assertions and expectation methods added between PHPUnit 4.8 - 9.5.
+ *
+ * See {@link https://github.com/Yoast/PHPUnit-Polyfills} for full
+ * documentation on the available polyfills.
+ */
+abstract class PHPUnit_Adapter_TestCase extends PHPUnit\Framework\TestCase {
+
+	use AssertAttributeHelper;
+	use AssertClosedResource;
+	use AssertEqualsSpecializations;
+	use AssertFileDirectory;
+	use AssertFileEqualsSpecializations;
+	use AssertionRenames;
+	use AssertIsType;
+	use AssertNumericType;
+	use AssertObjectEquals;
+	use AssertStringContains;
+	use EqualToSpecializations;
+	use ExpectException;
+	use ExpectExceptionMessageMatches;
+	use ExpectExceptionObject;
+	use ExpectPHPException;
+}

tests/phpunit/includes/testcase.php

@@ -1,48 +1,7 @@
 <?php
-
-use Yoast\PHPUnitPolyfills\Helpers\AssertAttributeHelper;
-use Yoast\PHPUnitPolyfills\Polyfills\AssertClosedResource;
-use Yoast\PHPUnitPolyfills\Polyfills\AssertEqualsSpecializations;
-use Yoast\PHPUnitPolyfills\Polyfills\AssertFileDirectory;
-use Yoast\PHPUnitPolyfills\Polyfills\AssertFileEqualsSpecializations;
-use Yoast\PHPUnitPolyfills\Polyfills\AssertionRenames;
-use Yoast\PHPUnitPolyfills\Polyfills\AssertIsType;
-use Yoast\PHPUnitPolyfills\Polyfills\AssertNumericType;
-use Yoast\PHPUnitPolyfills\Polyfills\AssertObjectEquals;
-use Yoast\PHPUnitPolyfills\Polyfills\AssertStringContains;
-use Yoast\PHPUnitPolyfills\Polyfills\EqualToSpecializations;
-use Yoast\PHPUnitPolyfills\Polyfills\ExpectException;
-use Yoast\PHPUnitPolyfills\Polyfills\ExpectExceptionMessageMatches;
-use Yoast\PHPUnitPolyfills\Polyfills\ExpectExceptionObject;
-use Yoast\PHPUnitPolyfills\Polyfills\ExpectPHPException;
-
 /**
- * Basic abstract test class with PHPUnit cross-version adapter layer.
- *
- * This adapter layer polyfills all PHPUnit assertion and expectation
- * methods which were added between PHPUnit 4.8 - 9.5 to allow tests
- * to benefit from the full range of available PHPUnit methods.
- *
- * See {@link https://github.com/Yoast/PHPUnit-Polyfills} for full
- * documentation on the available polyfills.
+ * Basic abstract test class.
  *
  * All WordPress unit tests should inherit from this class.
  */
-class WP_UnitTestCase extends WP_UnitTestCase_Base {
-
-	use AssertAttributeHelper;
-	use AssertClosedResource;
-	use AssertEqualsSpecializations;
-	use AssertFileDirectory;
-	use AssertFileEqualsSpecializations;
-	use AssertionRenames;
-	use AssertIsType;
-	use AssertNumericType;
-	use AssertObjectEquals;
-	use AssertStringContains;
-	use EqualToSpecializations;
-	use ExpectException;
-	use ExpectExceptionMessageMatches;
-	use ExpectExceptionObject;
-	use ExpectPHPException;
-}
+abstract class WP_UnitTestCase extends WP_UnitTestCase_Base {}