test(server): Add unit tests for server.js error handling paths

Add mocked unit tests covering the previously untested error-handling
functions in lib/server.js: the HTTP server error event handler,
buildServer error event forwarding, and the close() rejection handler
when buildServer.destroy() fails.

Author: RandomByte

packages/server/test/lib/server/server.js

@@ -0,0 +1,141 @@
+import test from "ava";
+import sinon from "sinon";
+import esmock from "esmock";
+import {EventEmitter} from "node:events";
+
+function createMockGraph(mockBuildServer) {
+	const mockProject = {
+		getName: sinon.stub().returns("test.project"),
+		getSourceReader: sinon.stub().returns({})
+	};
+	return {
+		getRoot: sinon.stub().returns(mockProject),
+		traverseBreadthFirst: sinon.stub().resolves(),
+		getProject: sinon.stub().returns(null),
+		serve: sinon.stub().resolves(mockBuildServer)
+	};
+}
+
+function createMockBuildServer() {
+	const buildServer = new EventEmitter();
+	buildServer.getRootReader = sinon.stub().returns({});
+	buildServer.getDependenciesReader = sinon.stub().returns({});
+	buildServer.getReader = sinon.stub().returns({});
+	buildServer.destroy = sinon.stub().resolves();
+	return buildServer;
+}
+
+function createMockServer() {
+	const mockServer = new EventEmitter();
+	mockServer.close = sinon.stub().callsFake((cb) => cb());
+	return mockServer;
+}
+
+function createMocks(mockServer) {
+	const mockApp = {
+		use: sinon.stub(),
+		listen: sinon.stub().callsFake((options, cb) => {
+			process.nextTick(cb);
+			return mockServer;
+		})
+	};
+
+	return {
+		"express": sinon.stub().returns(mockApp),
+		"portscanner": {
+			findAPortNotInUse: sinon.stub().callsFake((port, portMax, host, cb) => {
+				cb(null, port);
+			})
+		},
+		"../../../lib/middleware/MiddlewareManager.js": {
+			default: class MockMiddlewareManager {
+				applyMiddleware() {}
+			}
+		},
+		"@ui5/fs/resourceFactory": {
+			createReaderCollection: sinon.stub().returns({})
+		},
+		"@ui5/fs/ReaderCollectionPrioritized": {
+			default: class MockReaderCollectionPrioritized {}
+		}
+	};
+}
+
+test("server.on('error') rejects the serve promise", async (t) => {
+	const mockServer = createMockServer();
+	const mockBuildServer = createMockBuildServer();
+	const testError = new Error("server error");
+
+	const mockApp = {
+		use: sinon.stub(),
+		listen: sinon.stub().callsFake((options, cb) => {
+			// Emit error before the listen callback fires so reject() is called
+			process.nextTick(() => {
+				mockServer.emit("error", testError);
+			});
+			return mockServer;
+		})
+	};
+
+	const mocks = {
+		"express": sinon.stub().returns(mockApp),
+		"portscanner": {
+			findAPortNotInUse: sinon.stub().callsFake((port, portMax, host, cb) => {
+				cb(null, port);
+			})
+		},
+		"../../../lib/middleware/MiddlewareManager.js": {
+			default: class MockMiddlewareManager {
+				applyMiddleware() {}
+			}
+		},
+		"@ui5/fs/resourceFactory": {
+			createReaderCollection: sinon.stub().returns({})
+		},
+		"@ui5/fs/ReaderCollectionPrioritized": {
+			default: class MockReaderCollectionPrioritized {}
+		}
+	};
+
+	const {serve} = await esmock("../../../lib/server.js", mocks);
+	const graph = createMockGraph(mockBuildServer);
+	const error = await t.throwsAsync(serve(graph, {port: 3000}));
+	t.is(error, testError);
+});
+
+
+test("buildServer 'error' event is forwarded to error callback", async (t) => {
+	const mockServer = createMockServer();
+	const mockBuildServer = createMockBuildServer();
+	const mocks = createMocks(mockServer);
+	const testError = new Error("build error");
+
+	const {serve} = await esmock("../../../lib/server.js", mocks);
+	const graph = createMockGraph(mockBuildServer);
+
+	const errorReceived = new Promise((resolve) => {
+		serve(graph, {port: 3000}, resolve).then(() => {
+			mockBuildServer.emit("error", testError);
+		});
+	});
+
+	const err = await errorReceived;
+	t.is(err, testError);
+});
+
+test("close() still calls server.close when buildServer.destroy() rejects", async (t) => {
+	const mockServer = createMockServer();
+	const mockBuildServer = createMockBuildServer();
+	const mocks = createMocks(mockServer);
+
+	mockBuildServer.destroy = sinon.stub().rejects(new Error("destroy failed"));
+
+	const {serve} = await esmock("../../../lib/server.js", mocks);
+	const graph = createMockGraph(mockBuildServer);
+	const result = await serve(graph, {port: 3000});
+
+	await new Promise((resolve) => {
+		result.close(resolve);
+	});
+	t.true(mockServer.close.calledOnce, "server.close was called despite destroy rejection");
+});