test(shared-ini-file-loader): use jest.isolatedModules in slurpFile (#3442)

Author: trivikr

packages/shared-ini-file-loader/src/slurpFile.spec.ts

@@ -1,64 +1,72 @@
-describe("slurpFile", () => {
-  let slurpFile;
-  let mockReadFile;
+// ToDo: Change to "fs/promises" when supporting nodejs>=14
+import { promises } from "fs";
+
+jest.mock("fs", () => ({ promises: { readFile: jest.fn() } }));
 
+describe("slurpFile", () => {
   const UTF8 = "utf8";
   const getMockFileContents = (path: string, options = UTF8) => JSON.stringify({ path, options });
 
   beforeEach(() => {
-    mockReadFile = jest.fn().mockImplementation((path, options) => Promise.resolve(getMockFileContents(path, options)));
-    jest.mock("fs", () => ({ promises: { readFile: mockReadFile } }));
-
-    const slurpFileRequire = require("./slurpFile");
-    slurpFile = slurpFileRequire.slurpFile;
+    (promises.readFile as jest.Mock).mockImplementation((path, options) =>
+      Promise.resolve(getMockFileContents(path, options))
+    );
   });
 
   afterEach(() => {
     jest.clearAllMocks();
-    jest.resetModules();
   });
 
-  it("makes one readFile call for a filepath irrepsective of slurpFile calls", async () => {
-    const mockPath = "/mock/path";
-    const mockPathContent = getMockFileContents(mockPath);
+  it("makes one readFile call for a filepath irrepsective of slurpFile calls", (done) => {
+    jest.isolateModules(async () => {
+      const { slurpFile } = require("./slurpFile");
+      const mockPath = "/mock/path";
+      const mockPathContent = getMockFileContents(mockPath);
 
-    expect(mockReadFile).not.toHaveBeenCalled();
-    const fileContentArr = await Promise.all([slurpFile(mockPath), slurpFile(mockPath)]);
-    expect(fileContentArr).toStrictEqual([mockPathContent, mockPathContent]);
+      expect(promises.readFile).not.toHaveBeenCalled();
+      const fileContentArr = await Promise.all([slurpFile(mockPath), slurpFile(mockPath)]);
+      expect(fileContentArr).toStrictEqual([mockPathContent, mockPathContent]);
 
-    // There is one readFile call even through slurpFile is called in parallel twice.
-    expect(mockReadFile).toHaveBeenCalledTimes(1);
-    expect(mockReadFile).toHaveBeenCalledWith(mockPath, UTF8);
+      // There is one readFile call even through slurpFile is called in parallel twice.
+      expect(promises.readFile).toHaveBeenCalledTimes(1);
+      expect(promises.readFile).toHaveBeenCalledWith(mockPath, UTF8);
 
-    const fileContent = await slurpFile(mockPath);
-    expect(fileContent).toStrictEqual(mockPathContent);
+      const fileContent = await slurpFile(mockPath);
+      expect(fileContent).toStrictEqual(mockPathContent);
 
-    // There is one readFile call even through slurpFile is called for the third time.
-    expect(mockReadFile).toHaveBeenCalledTimes(1);
+      // There is one readFile call even through slurpFile is called for the third time.
+      expect(promises.readFile).toHaveBeenCalledTimes(1);
+      done();
+    });
   });
 
-  it("makes multiple readFile calls with based on filepaths", async () => {
-    const mockPath1 = "/mock/path/1";
-    const mockPathContent1 = getMockFileContents(mockPath1);
+  it("makes multiple readFile calls with based on filepaths", (done) => {
+    jest.isolateModules(async () => {
+      const { slurpFile } = require("./slurpFile");
+
+      const mockPath1 = "/mock/path/1";
+      const mockPathContent1 = getMockFileContents(mockPath1);
 
-    const mockPath2 = "/mock/path/2";
-    const mockPathContent2 = getMockFileContents(mockPath2);
+      const mockPath2 = "/mock/path/2";
+      const mockPathContent2 = getMockFileContents(mockPath2);
 
-    expect(mockReadFile).not.toHaveBeenCalled();
-    const fileContentArr = await Promise.all([slurpFile(mockPath1), slurpFile(mockPath2)]);
-    expect(fileContentArr).toStrictEqual([mockPathContent1, mockPathContent2]);
+      expect(promises.readFile).not.toHaveBeenCalled();
+      const fileContentArr = await Promise.all([slurpFile(mockPath1), slurpFile(mockPath2)]);
+      expect(fileContentArr).toStrictEqual([mockPathContent1, mockPathContent2]);
 
-    // There are two readFile calls as slurpFile is called in parallel with different filepaths.
-    expect(mockReadFile).toHaveBeenCalledTimes(2);
-    expect(mockReadFile).toHaveBeenNthCalledWith(1, mockPath1, UTF8);
-    expect(mockReadFile).toHaveBeenNthCalledWith(2, mockPath2, UTF8);
+      // There are two readFile calls as slurpFile is called in parallel with different filepaths.
+      expect(promises.readFile).toHaveBeenCalledTimes(2);
+      expect(promises.readFile).toHaveBeenNthCalledWith(1, mockPath1, UTF8);
+      expect(promises.readFile).toHaveBeenNthCalledWith(2, mockPath2, UTF8);
 
-    const fileContent1 = await slurpFile(mockPath1);
-    expect(fileContent1).toStrictEqual(mockPathContent1);
-    const fileContent2 = await slurpFile(mockPath2);
-    expect(fileContent2).toStrictEqual(mockPathContent2);
+      const fileContent1 = await slurpFile(mockPath1);
+      expect(fileContent1).toStrictEqual(mockPathContent1);
+      const fileContent2 = await slurpFile(mockPath2);
+      expect(fileContent2).toStrictEqual(mockPathContent2);
 
-    // There is one readFile call even through slurpFile is called for the third time.
-    expect(mockReadFile).toHaveBeenCalledTimes(2);
+      // There is one readFile call even through slurpFile is called for the third time.
+      expect(promises.readFile).toHaveBeenCalledTimes(2);
+      done();
+    });
   });
 });