Add comment to serveResource test

The resource is drained because it is piped in the serveResources
middleware. Therefore the getStream and pipe functionality is stubbed.
Such that its content can be compared in the test.

test/lib/server/middleware/serveResources.js

@@ -13,7 +13,7 @@ const writeResource = function(writer, path, size, stringContent) {
 		}
 	};
 	const resource = resourceFactory.createResource({path, buffer: Buffer.from(stringContent, "latin1"), statInfo});
-	// stub resource native functionality to make serveResources (middleware) run to the end
+	// stub resource functionality in order to be able to get the Resource's content. Otherwise it would be drained.
 	sinon.stub(resource, "getStream").returns({
 		pipe: function() {
 		}
@@ -28,6 +28,11 @@ const fakeResponse = {
 	setHeader: function(string, header) {}
 };
 
+test.afterEach.always((t) => {
+	sinon.restore();
+});
+
+
 test.serial("Check if properties file is served properly", (t) => {
 	t.plan(4);
 
@@ -48,7 +53,7 @@ test.serial("Check if properties file is served properly", (t) => {
 			}
 		});
 
-		const response = Object.assign({}, fakeResponse);
+		const response = fakeResponse;
 
 		const setHeaderSpy = sinon.spy(response, "setHeader");
 		const req = {
@@ -90,7 +95,7 @@ test.serial("Check if properties file is served properly with UTF-8", (t) => {
 			}
 		});
 
-		const response = Object.assign({}, fakeResponse);
+		const response = fakeResponse;
 
 		const setHeaderSpy = sinon.spy(response, "setHeader");
 		const req = {
@@ -125,15 +130,15 @@ test.serial("Check if properties file is served properly without property settin
 			}
 		});
 
-		const response = Object.assign({}, fakeResponse);
+		const response = fakeResponse;
 
 		const setHeaderSpy = sinon.spy(response, "setHeader");
 		const req = {
 			url: "/myFile3.properties",
 			headers: {}
 		};
 		const next = function(err) {
-			throw new Error(`Next callback called with error: ${err.message}`);
+			throw new Error(`Next callback called with error: ${err.stack}`);
 		};
 		return middleware(req, response, next).then((o) => {
 			return resource.getString();