add test case

test/Watch.test.js

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+"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);
+	});
+});

test/fixtures/watch/node_modules/inline-loader/index.js

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+module.exports = function(x) {
+	return x;
+}

test/fixtures/watch/node_modules/inline-loader/package.json

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+{
+  "name": "inline-loader",
+  "version": "1.0.0"
+}

test/fixtures/watch/node_modules/nested-package1/package.json

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+{
+  "name": "nested-package1",
+  "version": "1.0.0"
+}

test/fixtures/watch/node_modules/package/index.js

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+import "nested-package1";
+import "nested-package2";
+import "inline-loader!nested-package1";
+import "inline-loader!nested-package2";

test/fixtures/watch/node_modules/package/node_modules/nested-package2/package.json

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+{
+  "name": "nested-package2",
+  "version": "1.0.0"
+}

test/fixtures/watch/node_modules/package/package.json

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+{
+  "name": "package",
+  "version": "1.0.0"
+}

test/fixtures/watch/node_modules/some-loader/index.js

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+module.exports = function(x) {
+	return x;
+}

test/fixtures/watch/node_modules/some-loader/package.json

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+{
+  "name": "some-loader",
+  "version": "1.0.0"
+}

test/fixtures/watch/src/index.js

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+import "package";
+import "inline-loader!package";
+
+import "./local";
+import "inline-loader!./local";

test/fixtures/watch/src/local.js

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+import "package";
+import "inline-loader!package";