Tests: Stop using deprecated setMethods method (#427)

* Tests: Stop using deprecated setMethods method

Use `onlyMethods()` instead, which ensures that the method that is being mocked does exist in the class being mocked.

* Tests: use onlyMethods() only if it exists

tests/Unit/Integrations/IntegrationsTest.php

@@ -52,7 +52,13 @@ public function test_an_integration_can_be_registered_to_a_new_Integrations_obje
 	 * @uses \Parsely\Integrations\Integrations::register
 	 */
 	public function test_registered_integrations_have_their_integrate_method_called(): void {
-		$mock_integration = $this->getMockBuilder( Integration::class )->setMethods( array( 'integrate' ) )->getMock();
+		$mock_builder = $this->getMockBuilder( Integration::class );
+		// See https://github.com/Parsely/wp-parsely/issues/426.
+		if ( method_exists( $mock_builder, 'onlyMethods' ) ) {
+			$mock_integration = $mock_builder->onlyMethods( array( 'integrate' ) )->getMock();
+		} else {
+			$mock_integration = $mock_builder->setMethods( array( 'integrate' ) )->getMock();
+		}
 		$mock_integration->expects( $this->once() )->method( 'integrate' );
 
 		$integrations = new Integrations();