Feature/dependencies test trait (#405)

* Add new Dependency_Assertions trait

* Fix linting

src/mantle/testing/concerns/trait-dependency-assertions.php

@@ -0,0 +1,68 @@
+<?php //phpcs:disable WordPress.NamingConventions.ValidFunctionName.MethodNameInvalid
+/**
+ * Dependency_Assertions trait file
+ *
+ * @package Mantle
+ */
+
+namespace Mantle\Testing\Concerns;
+
+use PHPUnit\Framework\Assert as PHPUnit;
+use Mantle\Support\Collection;
+
+trait Dependency_Assertions {
+
+	/**
+	 * Asserts that the contents of an array are loaded prior to testing.
+	 *
+	 * Array can be an array of strings or an array of arrays where the first value is a string -- for instance,
+	 * a data provider.
+	 *
+	 * @param array $dependencies Dependencies array.
+	 */
+	public static function assertDependenciesLoaded( array $dependencies ) {
+		if ( count( $dependencies ) === 0 ) {
+			PHPUnit::markTestIncomplete( 'Asserting an empty dependency array has been loaded does not assert that no dependencies have been loaded.' );
+		}
+
+		foreach ( $dependencies as $dependency ) {
+			if ( is_array( $dependency ) ) {
+				$dependency = array_shift( $dependency );
+			}
+
+			if ( ! is_string( $dependency ) ) {
+				PHPUnit::fail( 'Dependency type not string.' );
+				continue;
+			}
+
+			self::assertDependencyLoaded( $dependency );
+		}
+	}
+
+	/**
+	 * Asserts that a file is loaded.
+	 *
+	 * @param string $dependency The dependency file name.
+	 */
+	public static function assertDependencyLoaded( string $dependency ) {
+		static $includes;
+
+		if (
+			! is_array( $includes ) ||
+			empty( $includes )
+		) {
+			$includes = new Collection( get_included_files() );
+		}
+
+		PHPUnit::assertTrue(
+			$includes
+				->filter( fn( $file ) => strpos( $file, $dependency ) !== false )
+				->count() > 0,
+			sprintf(
+				'%s dependency not found in included files.',
+				(string) $dependency
+			)
+		);
+	}
+
+}