Updated the files.

my-app/node_modules/err-code/test/.eslintrc.json

@@ -0,0 +1,5 @@
+{
+    "env": {
+        "mocha": true
+    }
+}

my-app/node_modules/err-code/test/test.js

@@ -0,0 +1,159 @@
+'use strict';
+
+const errcode = require('../index');
+const expect = require('expect.js');
+
+describe('errcode', () => {
+    describe('string as first argument', () => {
+        it('should throw an error', () => {
+            expect(() => { errcode('my message'); }).to.throwError((err) => {
+                expect(err).to.be.a(TypeError);
+            });
+        });
+    });
+
+    describe('error as first argument', () => {
+        it('should accept an error and do nothing', () => {
+            const myErr = new Error('my message');
+            const err = errcode(myErr);
+
+            expect(err).to.be(myErr);
+            expect(err.hasOwnProperty(err.code)).to.be(false);
+        });
+
+        it('should accept an error and add a code', () => {
+            const myErr = new Error('my message');
+            const err = errcode(myErr, 'ESOME');
+
+            expect(err).to.be(myErr);
+            expect(err.code).to.be('ESOME');
+        });
+
+        it('should accept an error object and add code & properties', () => {
+            const myErr = new Error('my message');
+            const err = errcode(myErr, 'ESOME', { foo: 'bar', bar: 'foo' });
+
+            expect(err).to.be.an(Error);
+            expect(err.code).to.be('ESOME');
+            expect(err.foo).to.be('bar');
+            expect(err.bar).to.be('foo');
+        });
+
+        it('should create an error object without code but with properties', () => {
+            const myErr = new Error('my message');
+            const err = errcode(myErr, { foo: 'bar', bar: 'foo' });
+
+            expect(err).to.be.an(Error);
+            expect(err.code).to.be(undefined);
+            expect(err.foo).to.be('bar');
+            expect(err.bar).to.be('foo');
+        });
+
+        it('should set a non-writable field', () => {
+            const myErr = new Error('my message');
+
+            Object.defineProperty(myErr, 'code', {
+                value: 'derp',
+                writable: false,
+            });
+            const err = errcode(myErr, 'ERR_WAT');
+
+            expect(err).to.be.an(Error);
+            expect(err.stack).to.equal(myErr.stack);
+            expect(err.code).to.be('ERR_WAT');
+        });
+
+        it('should add a code to frozen object', () => {
+            const myErr = new Error('my message');
+            const err = errcode(Object.freeze(myErr), 'ERR_WAT');
+
+            expect(err).to.be.an(Error);
+            expect(err.stack).to.equal(myErr.stack);
+            expect(err.code).to.be('ERR_WAT');
+        });
+
+        it('should to set a field that throws at assignment time', () => {
+            const myErr = new Error('my message');
+
+            Object.defineProperty(myErr, 'code', {
+                enumerable: true,
+                set() {
+                    throw new Error('Nope!');
+                },
+                get() {
+                    return 'derp';
+                },
+            });
+            const err = errcode(myErr, 'ERR_WAT');
+
+            expect(err).to.be.an(Error);
+            expect(err.stack).to.equal(myErr.stack);
+            expect(err.code).to.be('ERR_WAT');
+        });
+
+        it('should retain error type', () => {
+            const myErr = new TypeError('my message');
+
+            Object.defineProperty(myErr, 'code', {
+                value: 'derp',
+                writable: false,
+            });
+            const err = errcode(myErr, 'ERR_WAT');
+
+            expect(err).to.be.a(TypeError);
+            expect(err.stack).to.equal(myErr.stack);
+            expect(err.code).to.be('ERR_WAT');
+        });
+
+        it('should add a code to a class that extends Error', () => {
+            class CustomError extends Error {
+                set code(val) {
+                    throw new Error('Nope!');
+                }
+            }
+
+            const myErr = new CustomError('my message');
+
+            Object.defineProperty(myErr, 'code', {
+                value: 'derp',
+                writable: false,
+                configurable: false,
+            });
+            const err = errcode(myErr, 'ERR_WAT');
+
+            expect(err).to.be.a(CustomError);
+            expect(err.stack).to.equal(myErr.stack);
+            expect(err.code).to.be('ERR_WAT');
+
+            // original prototype chain should be intact
+            expect(() => {
+                const otherErr = new CustomError('my message');
+
+                otherErr.code = 'derp';
+            }).to.throwError();
+        });
+
+        it('should support errors that are not Errors', () => {
+            const err = errcode({
+                message: 'Oh noes!',
+            }, 'ERR_WAT');
+
+            expect(err.message).to.be('Oh noes!');
+            expect(err.code).to.be('ERR_WAT');
+        });
+    });
+
+    describe('falsy first arguments', () => {
+        it('should not allow passing null as the first argument', () => {
+            expect(() => { errcode(null); }).to.throwError((err) => {
+                expect(err).to.be.a(TypeError);
+            });
+        });
+
+        it('should not allow passing undefined as the first argument', () => {
+            expect(() => { errcode(undefined); }).to.throwError((err) => {
+                expect(err).to.be.a(TypeError);
+            });
+        });
+    });
+});