add test case

test/Watch.test.js

@@ -0,0 +1,61 @@
+"use strict";
+
+require("./helpers/warmup-webpack");
+
+const path = require("path");
+const webpack = require("..");
+const { createFsFromVolume, Volume } = require("memfs");
+
+describe("Watch", () => {
+	jest.setTimeout(10000);
+
+	it("should only compile a single time", done => {
+		let counterBeforeCompile = 0;
+		let counterDone = 0;
+		let counterHandler = 0;
+		const compiler = webpack(
+			{
+				context: path.resolve(__dirname, "fixtures/watch"),
+				watch: true,
+				mode: "development",
+				snapshot: {
+					managedPaths: [/^(.+?[\\/]node_modules[\\/])/]
+				},
+				experiments: {
+					futureDefaults: true
+				},
+				module: {
+					// unsafeCache: false,
+					rules: [
+						{
+							test: /\.js$/,
+							use: "some-loader"
+						}
+					]
+				},
+				plugins: [
+					c => {
+						c.hooks.beforeCompile.tap("test", () => {
+							counterBeforeCompile++;
+						});
+						c.hooks.done.tap("test", () => {
+							counterDone++;
+						});
+					}
+				]
+			},
+			(err, stats) => {
+				if (err) return done(err);
+				if (stats.hasErrors()) return done(new Error(stats.toString()));
+				counterHandler++;
+			}
+		);
+		compiler.outputFileSystem = createFsFromVolume(new Volume());
+		setTimeout(() => {
+			expect(counterBeforeCompile).toBe(1);
+			expect(counterDone).toBe(1);
+			expect(counterHandler).toBe(1);
+			compiler.close(done);
+		}, 5000);
+	});
+});