Example single-file gulp setup

gulpfile.js

import {src, dest, watch, parallel, series} from 'gulp';
import lintPlugin from 'gulp-lint-plugin';
import testPlugin from 'gulp-test-plugin';
import buildPlugin from 'gulp-build-plugin';

const SRC_DIRECTORY = './src';
const TEST_DIRECTORY = './test';
const DIST_DIRECTORY = './dist';

const lintDir = dir => src(dir)
  .pipe(lintPlugin());

const lintSrc = () => lintDir(SRC_DIRECTORY);
const lintTest = () => lintDir(TEST_DIRECTORY);
const lintFiles = parallel(lintSrc, lintTest);

const testFiles = () => src(TEST_DIRECTORY)
  .pipe(testPlugin());

const reportLint = () => lintPlugin.report();
const reportTest = () => testPlugin.report();
const reportLintAndTest = series(reportLint, reportTest);

const buildFiles = () => src(SRC_DIRECTORY)
  .pipe(buildPlugin())
  .pipe(dest(DIST_DIRECTORY));

export const lint = series(lintFiles, reportLint);
export const test = series(parallel(lint, testFiles), reportLintAnTest);
export const build = series(test, buildFiles);
export const dev = () => {
  watch(SRC_DIRECTORY, parallel(test, build));
  watch(TEST_DIRECTORY, test);
};

export default dev;