Build/Test Tools: Add support for PHPUnit 7.x.

* Create an abstract `WP_UnitTestCase_Base` class to share between PHPUnit 7.x and older versions.
* Add a speed-trap loader to determine which `SpeedTrapListener` class needs to be loaded for the current PHPUnit version.
* Remove unnecessary `PHPUnit\Util\Test` and `PHPUnit_Util_Getopt` inheritances.
* Update Travis CI config to use PHPUnit 7.x for PHP 7.1, 7.2, and nightly PHP versions.

Props jipmoors, netweb, desrosj, ayeshrajans, soulseekah, SergeyBiryukov.
See #43218.

git-svn-id: https://develop.svn.wordpress.org/trunk@44701 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/includes/phpunit7/testcase.php

@@ -0,0 +1,31 @@
+<?php
+
+require_once dirname( dirname( __FILE__ ) ) . '/abstract-testcase.php';
+
+/**
+ * Defines a basic fixture to run multiple tests.
+ *
+ * Resets the state of the WordPress installation before and after every test.
+ *
+ * Includes utility functions and assertions useful for testing WordPress.
+ *
+ * All WordPress unit tests should inherit from this class.
+ */
+class WP_UnitTestCase extends WP_UnitTestCase_Base {
+	/**
+	 * Asserts that a condition is not false.
+	 *
+	 * This method has been backported from a more recent PHPUnit version, as tests running on PHP 5.2 use
+	 * PHPUnit 3.6.x.
+	 *
+	 * @since 4.7.4
+	 *
+	 * @param bool   $condition Condition to check.
+	 * @param string $message   Optional. Message to display when the assertion fails.
+	 *
+	 * @throws PHPUnit_Framework_AssertionFailedError
+	 */
+	public static function assertNotFalse( $condition, string $message = '' ): void {
+		self::assertThat( $condition, self::logicalNot( self::isFalse() ), $message );
+	}
+}