Add template files for plugin examples and tests

lib/generate-plugin/templates/examples/simple/src/index.js.tpl

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+import esmModule from './static-esm-module';
+
+const getLazyModule = () => System.import('./lazy-module');
+
+setTimeout(() => {
+  getLazyModule.then((modDefault) => {
+    console.log(modDefault); //eslint-disable-line
+  });
+}, 300);
+
+console.log(esmModule); //eslint-disable-line

lib/generate-plugin/templates/examples/simple/src/lazy-module.js.tpl

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+export default 'lazy';

lib/generate-plugin/templates/examples/simple/src/static-esm-module.js.tpl

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+export default 'foo';

lib/generate-plugin/templates/examples/simple/webpack.config.js.tpl

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+const path = require('path');
+const <%= name %> = require('../../src/index.js');
+
+module.exports = {
+  entry: './src/index.js',
+  output: {
+    path: path.join(__dirname, 'example_dist'),
+    filename: '[name].chunk.js',
+  },
+  plugins: [
+    new <%= name %>()
+  ]
+};

lib/generate-plugin/templates/test/fixtures/simple-file.js.tpl

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+import foo from "./foo"; // eslint-disable-line
+
+console.log(foo);

lib/generate-plugin/templates/test/functional.test.js.tpl

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+import {
+	runWebpackExampleInMemory,
+} from '../test/test-utils';
+
+test('should run with no errors or warnings', async () => {
+	const buildStats = await runWebpackExampleInMemory('simple');
+	const { errors, warnings } = buildStats;
+
+	expect([...errors, ...warnings].length).toBe(0);
+});

lib/generate-plugin/templates/test/test-utils.js.tpl

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+import path from 'path';
+import webpack from 'webpack';
+import Promise from 'bluebird';
+import MemoryFs from 'memory-fs';
+
+const fs = new MemoryFs();
+const unitTestFixtures = path.resolve(__dirname, 'fixtures');
+
+/**
+ *
+ *
+ * @param {string} fixtureName
+ * @param {string} [withQueryString='']
+ * @returns {string} Absolute path of a file with query that is to be run by a loader.
+ */
+function getFixtureResource(fixtureName, withQueryString = '') {
+	return `${getFixture(fixtureName)}?${withQueryString}`;
+}
+
+/**
+ *
+ *
+ * @param {string} fixtureName
+ * @returns {string} Absolute path of a file with query that is to be run by a loader.
+ */
+function getFixture(fixtureName) {
+	return path.resolve(unitTestFixtures, `${fixtureName}.js`);
+}
+
+/**
+ *
+ *
+ * @param {Object} withOptions - Loader Options
+ * @returns {{loader: string, options: Object}}
+ */
+function getLoader(withOptions) {
+	return [{ loader: path.resolve(__dirname, '../dist/index.js'), options: withOptions }];
+}
+
+/**
+ *
+ *
+ * @param {string} exampleName
+ * @returns {Object|Array} - Returns an object or array of objects representing the webpack configuration options
+ */
+function getExampleConfig(exampleName) {
+	return require(`../examples/${exampleName}/webpack.config.js`); //eslint-disable-line
+}
+
+/**
+ *
+ *
+ * @param {string} exampleName - name of example inside of examples folder
+ * @returns
+ */
+async function runWebpackExampleInMemory(exampleName) {
+	const webpackConfig = getExampleConfig(exampleName);
+	const compiler = webpack(webpackConfig);
+
+	compiler.outputFileSystem = fs;
+
+	const run = Promise.promisify(compiler.run, { context: compiler });
+	const stats = await run();
+
+
+	const { compilation } = stats;
+	const { errors, warnings, assets, entrypoints, chunks, modules } = compilation;
+	const statsJson = stats.toJson();
+
+	return {
+		assets,
+		entrypoints,
+		errors,
+		warnings,
+		stats,
+		chunks,
+		modules,
+		statsJson,
+	};
+}
+
+export { getExampleConfig, runWebpackExampleInMemory, fs, getFixtureResource, getLoader, getFixture };