How to use the @ckeditor/ckeditor5-dev-utils.tools.copyFile function in @ckeditor/ckeditor5-dev-utils

const fileName = splitPath.slice( -1 ).join();
						const builtEditorPath = path.join( bundleDir, bundleConfig.path, bundleConfig.moduleName );
						const destinationPath = path.join.apply( null, [
							testPath,
							'tests',
							packageName,
							'samples',
							beginPath,
							'_assets',
							fileName
						] );

						// Copy editor builds to proper directory.
						return Promise.all( [
							tools.copyFile( `${ builtEditorPath }.js`, `${ destinationPath }.js` ),
							tools.copyFile( `${ builtEditorPath }.css`, `${ destinationPath }.css` )
						] );
					} )
					// And clean up.

_generateCssBundle( { sourceBuildDir, fileName, filePath } ) {
		const cssSource = path.join( sourceBuildDir, 'theme', 'ckeditor.css' );
		const outputDirectory = path.dirname( filePath );

		return tools.copyFile( cssSource, path.join( outputDirectory, `${ fileName }.css` ) );
	},