feat: support mock class method from instance (#52)

* fix: read file on windows

README.md

@@ -306,6 +306,25 @@ req.on('error', function (err) {
 });
 ```
 
+### .classMethod(instance, method, mockMethod)
+
+```js
+class Foo {
+  async fetch() {
+    return 1;
+  }
+}
+
+const foo = new Foo();
+const foo1 = new Foo();
+
+mm.classMethod(foo, 'fetch', async () => {
+  return 3;
+});
+assert(await foo.fetch() === 3);
+assert(await foo1.fetch() === 3);
+```
+
 ## License
 
 ```

lib/es6.js

@@ -78,3 +78,8 @@ mm.errorOnce = function(mod, method, error, props, timeout) {
   });
   return this;
 };
+
+// mock class method from instance
+mm.classMethod = function(instance, property, value) {
+  return mm(instance.constructor.prototype, property, value);
+};

test/es6.js

@@ -1,5 +1,6 @@
 'use strict';
 
+const assert = require('assert');
 const mm = require('..');
 
 describe('test/es6.test.js', () => {
@@ -36,6 +37,45 @@ describe('test/es6.test.js', () => {
     });
   });
 
+  describe('classMethod()', () => {
+    it('should class method from instance', async () => {
+      class Foo {
+        async fetch() {
+          return 1;
+        }
+      }
+
+      const foo = new Foo();
+      const foo1 = new Foo();
+      assert(await foo.fetch() === 1);
+      assert(await foo1.fetch() === 1);
+
+      mm(foo, 'fetch', async () => {
+        return 2;
+      });
+      assert(await foo.fetch() === 2);
+      assert(await foo1.fetch() === 1);
+
+      mm.restore();
+      mm.classMethod(foo, 'fetch', async () => {
+        return 3;
+      });
+      assert(await foo.fetch() === 3);
+      assert(await foo1.fetch() === 3);
+
+      mm.restore();
+      mm.classMethod(foo, 'fetch', async () => {
+        return 4;
+      });
+      const foo2 = new Foo();
+      assert(await foo.fetch() === 4);
+      assert(await foo1.fetch() === 4);
+      assert(await foo2.fetch() === 4);
+      const foo3 = new Foo();
+      assert(await foo3.fetch() === 4);
+    });
+  });
+
   describe('error(), errorOnce()', () => {
     it('should mock error', function* () {
       mm.error(foo, 'getValue');

test/mm.test.js

@@ -138,15 +138,15 @@ describe('test/mm.test.js', () => {
   describe('error(), errorOnce()', () => {
     it('should mock fs.readFile return error', function(done) {
       mm.error(fs, 'readFile', 'can not read file');
-      fs.readFile('/etc/hosts', 'utf8', function(err, data) {
+      fs.readFile(__filename, 'utf8', function(err, data) {
         assert(err);
         err.name.should.equal('MockError');
         err.message.should.equal('can not read file');
         assert(!data);
 
         mm.restore();
 
-        fs.readFile('/etc/hosts', 'utf8', function(err, data) {
+        fs.readFile(__filename, 'utf8', function(err, data) {
           assert(!err);
           assert(data);
           data.should.containEql('127.0.0.1');
@@ -157,13 +157,13 @@ describe('test/mm.test.js', () => {
 
     it('should mock fs.readFile return error once', done => {
       mm.errorOnce(fs, 'readFile', 'can not read file');
-      fs.readFile('/etc/hosts', 'utf8', (err, data) => {
+      fs.readFile(__filename, 'utf8', (err, data) => {
         assert(err);
         err.name.should.equal('MockError');
         err.message.should.equal('can not read file');
         assert(!data);
 
-        fs.readFile('/etc/hosts', 'utf8', (err, data) => {
+        fs.readFile(__filename, 'utf8', (err, data) => {
           assert(!err);
           assert(data);
           data.should.containEql('127.0.0.1');
@@ -176,7 +176,7 @@ describe('test/mm.test.js', () => {
       const err = new Error('mock error instance');
       err.name = 'CustomError';
       mm.error(fs, 'readFile', err);
-      fs.readFile('/etc/hosts', 'utf8', function(err, data) {
+      fs.readFile(__filename, 'utf8', function(err, data) {
         assert(err);
         err.name.should.equal('CustomError');
         err.message.should.equal('mock error instance');
@@ -187,7 +187,7 @@ describe('test/mm.test.js', () => {
 
     it('should mock error with empty error', function(done) {
       mm.error(fs, 'readFile');
-      fs.readFile('/etc/hosts', 'utf8', function(err, data) {
+      fs.readFile(__filename, 'utf8', function(err, data) {
         assert(err);
         err.name.should.equal('MockError');
         err.message.should.equal('mm mock error');
@@ -198,7 +198,7 @@ describe('test/mm.test.js', () => {
 
     it('should mock error with properties', function(done) {
       mm.error(fs, 'readFile', 'mm mock error', { code: 'ENOENT', name: 'MockError' });
-      fs.readFile('/etc/hosts', 'utf8', function(err, data) {
+      fs.readFile(__filename, 'utf8', function(err, data) {
         assert(err);
         err.name.should.equal('MockError');
         err.message.should.equal('mm mock error');
@@ -211,7 +211,7 @@ describe('test/mm.test.js', () => {
     it('should mock error with 500ms timeout', function(done) {
       mm.error(fs, 'readFile', '500ms timeout', 500);
       const start = Date.now();
-      fs.readFile('/etc/hosts', 'utf8', function(err, data) {
+      fs.readFile(__filename, 'utf8', function(err, data) {
         const use = Date.now() - start;
         assert(err);
         err.name.should.equal('MockError');
@@ -225,7 +225,7 @@ describe('test/mm.test.js', () => {
     it('should mock error with 500ms timeout and properties', function(done) {
       mm.error(fs, 'readFile', '500ms timeout', { code: 'ENOENT' }, 500);
       const start = Date.now();
-      fs.readFile('/etc/hosts', 'utf8', function(err, data) {
+      fs.readFile(__filename, 'utf8', function(err, data) {
         const use = Date.now() - start;
         assert(err);
         err.name.should.equal('MockError');