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typemoq

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Simple mocking library for JavaScript targeting TypeScript development. If you have used before a library like Moq then the syntax should look familiar, otherwise the examples below should hopefully provide enough information to get you started quickly.

Features

  • Strongly typed
  • Auto complete/intellisense support
  • Static and dynamic mocking
  • Mock objects, classes (with arguments), constructor functions and interfaces
  • Control mock behavior
  • Record and replay expectations
  • Auto sandbox global objects and types
  • Support ECMAScript 5 and 6
  • Support node.js and browser

Sauce Test Status


Installing

Release version
npm install typemoq

Or add this NuGet dependency to your project:

PM> Install-Package typemoq 

The distribution directory should contain:

  • Compiled JavaScript: typemoq.js and its minified version typemoq-min.js
  • TypeScript definitions: typemoq.d.ts
Development version
npm install https://github.com/florinn/typemoq
Node.js
TypeScript 1.6 and later
import * as TypeMoq from "typemoq";
TypeScript pre 1.6
/// <reference path="./node_modules/typemoq/dist/typemoq.d.ts" />
TypeMoq = require("typemoq");
Browser

Include at the top of your script file:

/// <reference path="./node_modules/typemoq/dist/typemoq.d.ts" />
import * as TypeMoq from "typemoq";

TypeMoq requires some dependencies to run, so make sure to include them in your page before typemoq.js:

<script src="https://unpkg.com/circular-json/build/circular-json"></script>
<script src="https://unpkg.com/lodash"></script>
<script src="https://unpkg.com/typemoq"></script>

Also in your tsconfig.json you need to set the module target as UMD:

"compilerOptions": {
    ...
    "module": "UMD",
    ...
}

At this point you should have access in your script to a global variable named TypeMoq.

Usage

After importing TypeMoq into your project, the following types should be available:

Type Description
TypeMoq.Mock Used for creating 'regular' mocks (see Create mocks and Setup mocks)
TypeMoq.MockBehavior Used to specify how the mock should act when no expectations are defined (see Control mock behavior)
TypeMoq.It Helper for matching arguments (see Setup mocks and Verify expectations)
TypeMoq.Times Helper for performing verification (see Verify expectations)
TypeMoq.GlobalMock Used to create 'global' mocks corresponding to global objects (see Create global mocks)
TypeMoq.GlobalScope Used to create an execution context that makes use of any specified 'global' mocks (see Auto sandbox global mocks)
TypeMoq.MockException Exception thrown internally containing debug info

Create mocks

Static mocks

Static mocks can be created either from class types and constructor arguments or from existing objects, including function objects.

Using class types and constructor arguments
interface IBar {
  value: string;
  anyValue: any;
}
 
class Bar implements IBar {
  value: string = '';
  anyValue: any = undefined;
}
 
class Foo {
  constructor(private _bar: IBar) { this._bar = _bar || new Bar(); }
  
  get bar(): IBar { return this._bar; }
  do(stringValue: string) { return 'Foo.do:' + stringValue; }
  setBar(value: string) { this._bar.value = value; }
}
 
class GenericFoo<T> {
  private _bar: T;
 
  constructor(barCtor?: { new (): T }, public numberValue?: number) {
    this._bar = new barCtor(); 
  }
 
  get bar(): T { return this._bar; }
  do(stringValue: string) { return 'GenericFoo.do:' + stringValue + ': ' + this._bar.toString(); }
}
 
// Using class as constructor parameter
let mock: TypeMoq.IMock<Bar> = TypeMoq.Mock.ofType(Bar);
 
// Using class as constructor parameter and casting result to interface
let mock: TypeMoq.IMock<IBar> = TypeMoq.Mock.ofType(Bar);
 
// Using interface as type variable and class as constructor parameter
let mock: TypeMoq.IMock<IBar> = TypeMoq.Mock.ofType<IBar>(Bar);
 
// Using class as constructor parameter and constructor arguments
let bar = new Bar();
let mock: TypeMoq.IMock<Foo> = TypeMoq.Mock.ofType(Foo, TypeMoq.MockBehavior.Loose, bar);
 
// Using a generic class as constructor parameter and constructor arguments
let mock: TypeMoq.IMock<GenericFoo<Bar>> = TypeMoq.Mock.ofType(GenericFoo, TypeMoq.MockBehavior.Loose, Bar, 999);
Using existing objects, including function objects
function someFunc() {
  return "someFunc was called";
}
 
function someFuncWithArgs(a: any, b: any, c: any) {
  return "someFuncWithArgs was called";
}
 
// From an existing object
let bar = new Bar();
let mock: TypeMoq.IMock<Bar> = TypeMoq.Mock.ofInstance(bar);
 
// Or from function objects
let mock1: TypeMoq.IMock<() => string> = TypeMoq.Mock.ofInstance(someFunc);
let mock2: TypeMoq.IMock<(a: any, b: any, c: any)=>string> = TypeMoq.Mock.ofInstance(someFuncWithArgs);

Dynamic mocks

Dynamic mocking requires your runtime (browser or node.js) to support the Proxy global object added in ECMAScript 6. If Proxy is not detected, TypeMoq is going to throw a MockException.

A dynamic mock is created by specifying a type parameter. The following type parameters are supported:

// Using Function as type parameter
let mock: TypeMoq.IMock<Function> = TypeMoq.Mock.ofType<Function>();
  • a class type
// Using the 'instance' side of the class as type parameter
let mock: TypeMoq.IMock<Bar> = TypeMoq.Mock.ofType<Bar>();
 
// Specifying mock behavior
let mock: TypeMoq.IMock<Foo> = TypeMoq.Mock.ofType<Foo>(undefined, TypeMoq.MockBehavior.Loose);
  • a constructor function
// Using the 'static' side of the class as type parameter
let mock: TypeMoq.IMock<typeof Bar> = TypeMoq.Mock.ofType<typeof Bar>();
  • an interface type
// Using an interface as type parameter
let mock: TypeMoq.IMock<IBar> = TypeMoq.Mock.ofType<IBar>();

As opposed to static mocks, dynamic mocks have some limitations due to the absence of the underlying target instance:

  • No partial mocking
  • No embedded mocks passed as constructor arguments
  • Properties return by default a function object and not undefined
interface IThing {
  getA(a: string): string;
  getB(b: number): number;
  getC(): boolean;
  valueA: string;
}
 
let mock: TypeMoq.IMock<IThing> = TypeMoq.Mock.ofType<IThing>();
 
expect(mock.object.getA("abc")).to.be.undefined;
expect(mock.object.getB(123)).to.be.undefined;
expect(mock.object.getC()).to.be.undefined;
expect(mock.object.valueA).to.be.a("function");

As a workaround you may set the property to return undefined:

mock.setup(x => x.valueA).returns(() => undefined);
 
expect(mock.object.valueA).to.be.undefined;

Note: A mock (created in any of the ways listed above) exposes the actual mock object through the .object property (that has the same type as the class or object being mocked).

Setup mocks

Mocks allow to match functions, methods and properties and setup return callbacks or exceptions to throw.

setup accepts a function (also referred as 'matcher') taking as input argument the type being mocked and as body the value/property/method (with arguments if that's the case) to match.

Parameter matchers
Matcher Description
TypeMoq.It.isValue<T>(x: T) Performs deep comparison against the provided object or basic value
TypeMoq.It.isObjectWith<T>(x: Object) Performs partial deep comparison against the provided object
TypeMoq.It.isAny() Matches any type
TypeMoq.It.isAnyObject<T>(x: Ctor<T>) Matches any object compatible with the provided type
TypeMoq.It.isAnyString() Matches any string
TypeMoq.It.isAnyNumber() Matches any number
TypeMoq.It.is<T>(predicate: IFunc2<T, boolean>) Performs comparison using the provided predicate

If no matcher is specified then an implicit matcher is considered that performs strict equality deep comparison, equivalent to It.is(x => _.isEqual(x, a)).

Matching functions
// Match a no args function
let mock: TypeMoq.IMock<() => string> = TypeMoq.Mock.ofInstance(someFunc);
mock.setup(x => x()).returns(() => "At vero eos et accusamus");
 
// Match a function with args
let mock: TypeMoq.IMock<(a: any, b: any, c: any) => string> = TypeMoq.Mock.ofInstance(someFuncWithArgs);
mock.setup(x => x(TypeMoq.It.isAny(), TypeMoq.It.isAny(), TypeMoq.It.isAny())).returns(() => "At vero eos et accusamus");
Matching methods
class Doer {
  doVoid(): void { }
  doNumber(n?: number): number { return n || 101; }
  doString(s?: string): string { return s || 'xyz'; }
  doObject(o?: Object): Object { return o || new Object(); }
  doBar(b?: Bar): Bar { return b; }
}
 
let mock = TypeMoq.Mock.ofType(Doer);
 
// Match a no args method
mock.setup(x => x.doNumber());
 
// Match a method with explicit number value params
mock.setup(x => x.doNumber(TypeMoq.It.isValue(321)));
 
// Match a method with implicit number value params
mock.setup(x => x.doNumber(321));
 
// Match a method with explicit string value params
mock.setup(x => x.doString(TypeMoq.It.isValue("abc")));
 
// Match a method with implicit string value params
mock.setup(x => x.doString("abc"));
 
// Match a method with object value params
let bar = new Bar();
mock.setup(x => x.doObject(TypeMoq.It.isAnyObject(Bar)));
 
// Match a method with implicit object value params
const anObject = {};
mock.setup(x => x(anObject)).returns(() => 123);
expect(mock.object(anObject)).to.eq(123);
 
// Match a method with any string params
mock.setup(x => x.doString(TypeMoq.It.isAnyString()));
 
// Match a method with any number params
mock.setup(x => x.doNumber(TypeMoq.It.isAnyNumber()));
 
// Match a method with any interface/class params
let bar1 = new Bar();
let bar2 = new Bar();
mock.setup(x => x.doBar(TypeMoq.It.isAnyObject(Bar)));
 
// Match a method by a param predicate 
let bar1 = new Bar();
bar1.value = "Ut enim ad minim veniam";
let bar2 = new Bar();
let mock = TypeMoq.Mock.ofType(Doer);
 
mock.setup(x => x.doBar(It.is((x: Bar) => x.value === "Ut enim ad minim veniam"))).returns(() => bar2);

To be able to match the static methods of some class, you would need to create a dynamic mock of the type of the class itself. E.g.

class Greeter {
  private static _instance: Greeter | null;
  static instance(): Greeter {
    if (!this._instance) {
      this._instance = new Greeter();
    }
    return this._instance;
  } 
    
  greet(): string {
    return 'Hello';
  }
}
 
let greeter = Greeter.instance();
let mock: TypeMoq.IMock<typeof Greeter> = Typemoq.Mock.ofType<typeof Greeter>();
 
mock.setup(x => x.instance()).returns(() => greeter);
 
expect(mock.object.instance()).to.eq(greeter);
Matching properties
class FooWithPublicGetterAndSetter {
  private _foo: string;
  public get foo(): string { return this._foo; }
  public set foo(value: string) { this._foo = value; }
}
 
// Match a property getter
let mock = TypeMoq.Mock.ofType(FooWithPublicGetterAndSetter);
mock.setup(x => x.foo);
 
// Match a property setter
mock.object.foo = "Lorem ipsum dolor sit amet";
mock.verify(x => x.foo = It.isValue("Lorem ipsum dolor sit amet"), Times.atLeastOnce());

Note: To be able to match a property make sure the property is initialized. Otherwise the TypeScript compiler will omit the uninitialized property from the emitted JavaScript and hence TypeMoq will throw a MockException with an 'invalid setup expression' message.

class Baz {
  value: string = '';
  anyValue: any;
}
 
let mock = TypeMoq.Mock.ofType(Baz);
mock.setup(x => x.value);       // OK
mock.setup(x => x.anyValue);    // throws MockException - invalid setup expression
Matching objects
interface Baz {
  bar: string
  jaz: number  
}
 
class FooWithObjectArgMethod {
  private _foo: Object
  public foo(value: Object): void { }
}
 
let mock = TypeMoq.Mock.ofType(FooWithObjectArgMethod);
 
// Match object deeply
mock.setup(x => x.foo(It.isValue({ bar: 'hello', jaz: 42 })));
 
// Match object partially
mock.setup(x => x.foo(It.isObjectWith({ jaz: 42 })));
Attaching return callbacks

The callback attached to .returns has the same signature as the matching function/method.

Also the callback gets called with the arguments passed to the matching function/method and it must have the same return type, making possible the following:

mock.setup(x => x.doString("abc")).returns((s: string) => s.toUpperCase());
Attaching exceptions to throw
mock.setup(...).throws(new CustomException());

Attach callbacks

Attached callbacks are called before the .returns callback or .throws get called, and they have similar signature and behavior to .returns callbacks.

let mock = TypeMoq.Mock.ofType(Doer);
let called1, called2 = false;
let numberArg: number;
 
mock.setup(x => x.doString(TypeMoq.It.isAnyString())).callback(() => called1 = true).returns(s => s.toUpperCase());
mock.setup(x => x.doNumber(TypeMoq.It.isAnyNumber())).callback(n => { numberArg = n; called2 = true; }).returns(n => n + 1);

Record and replay

Mocks allow to "record" and "replay" one or more setups for the same matching function, method or property.

  • If a single setup is recorded then at replay it is always executed:
let mock = TypeMoq.Mock.ofInstance(() => -1);
 
// record
mock.setup(x => x()).returns(() => 0);
 
// replay
expect(mock.object()).to.eq(0);
expect(mock.object()).to.eq(0);
expect(mock.object()).to.eq(0);
  • If more setups are recorded then at replay they are executed in the order of registration:
let mock = TypeMoq.Mock.ofInstance(() => -1);
 
// record
mock.setup(x => x()).returns(() => 0);
mock.setup(x => x()).returns(() => 1);
mock.setup(x => x()).returns(() => 2);
 
// replay
expect(mock.object()).to.eq(0);
expect(mock.object()).to.eq(1);
expect(mock.object()).to.eq(2);
expect(mock.object()).to.eq(undefined);

In the latter case, when there are no more recorded setups left to play, the mock starts returning default values or raises MockException if MockBehavior.Strict (see Control mock behavior).

Reset mocks

Calling .reset() on a mock returns the mock to its initial state by removing any previous setups.

Control mock behavior

Using MockBehavior

When creating a mock, you may specify a behavior value such as:

  • MockBehavior.Loose (default) - never throws when no corresponding setup is found and just returns default values
  • MockBehavior.Strict - raises exceptions for anything that doesn't have a corresponding setup
let mock = TypeMoq.Mock.ofType(Doer, TypeMoq.MockBehavior.Strict);
Partial mocking

When the mock property callBase is set to true, if there's no overriding setup the mock invokes the object being mocked.

mock.callBase = true;

The default value of callBase is false, so by default when there's no overriding setup the mock returns undefined.

Verify expectations

Expectations can be verified either one by one or all at once by marking matchers as verifiable.

Expectations
Expectation Description
TypeMoq.Times.exactly(n: number) Called exactly n times
TypeMoq.Times.never() Never called
TypeMoq.Times.once() Called once
TypeMoq.Times.atLeastOnce() Called at least once (default value)
TypeMoq.Times.atMostOnce() Called at most once
Verify expectations one by one

To verify an expectation you can use the verify method and specify a matching function and an expectation.

// Verify that a no args function was called at least once
let mock: TypeMoq.IMock<() => string> = TypeMoq.Mock.ofInstance(someFunc);
mock.object();
mock.verify(x => x(), TypeMoq.Times.atLeastOnce());
 
// Verify that a function with args was called at least once
let mock: TypeMoq.IMock<(a: any, b: any, c: any) => string> = TypeMoq.Mock.ofInstance(someFuncWithArgs);
mock.object(1, 2, 3);
mock.verify(x => x(TypeMoq.It.isAnyNumber(), TypeMoq.It.isAnyNumber(), TypeMoq.It.isAnyNumber()), TypeMoq.Times.atLeastOnce());
 
// Verify that no args method was called at least once
let mock = TypeMoq.Mock.ofType(Doer);
mock.object.doVoid();
mock.verify(x => x.doVoid(), TypeMoq.Times.atLeastOnce());
 
// Verify that method with params was called at least once
let mock = TypeMoq.Mock.ofType(Doer);
mock.object.doString("Lorem ipsum dolor sit amet");
mock.verify(x => x.doString(TypeMoq.It.isValue("Lorem ipsum dolor sit amet")), TypeMoq.Times.atLeastOnce());
 
// Verify that value getter was called at least once
let mock = TypeMoq.Mock.ofType(Bar);
mock.object.value;
mock.verify(x => x.value, TypeMoq.Times.atLeastOnce());
 
// Verify that value setter was called at least once
let mock = TypeMoq.Mock.ofType(Bar);
mock.object.value = "Lorem ipsum dolor sit amet";
mock.verify(x => x.value = TypeMoq.It.isValue("Lorem ipsum dolor sit amet"), TypeMoq.Times.atLeastOnce());

Note:

  • When constructing a mock, it is allowed to pass mock objects as arguments and later verify expectations on them. E.g.:
let mockBar = TypeMoq.Mock.ofType(Bar);
let mockFoo = TypeMoq.Mock.ofType(Foo, TypeMoq.MockBehavior.Loose, mockBar.object);
mockFoo.callBase = true;
 
mockFoo.object.setBar("Lorem ipsum dolor sit amet");
 
mockBar.verify(x => x.value = TypeMoq.It.isValue("Lorem ipsum dolor sit amet"), TypeMoq.Times.atLeastOnce());
  • For static mocks, TypeMoq is able to verify any inner calls inside regular functions but not inside lambda ones. E.g.:
class FooBar {
  register(): void {
    this.canExecute();
  }
 
  registerLambda = () => {
    this.canExecute();
  }
 
  canExecute(): void {
    console.log("FooBar.canExecute() was called");
  }
}
 
let mock: TypeMoq.IMock<FooBar> = TypeMoq.Mock.ofType(FooBar);
mock.callBase = true;
 
mock.object.register();
mock.object.registerLambda();   // inside a lambda function calls cannot be verified
 
mock.verify(x => x.canExecute(), Times.once());
Verify all expectations at once

Instead of verifying one expectation at a time, you may specify the expectation at setup time by calling verifiable(times: Times) and then verifyAll() to check all expectations.

The default value of the times parameter is equal to Times.once().

mock.setup(x => x.doNumber(999)).verifiable(); // Times.once()
mock.setup(x => x.doString(It.isAny())).verifiable(Times.exactly(2));
mock.setup(x => x.doVoid()).verifiable(Times.atMostOnce());
 
mock.object.doVoid();
mock.object.doString("Lorem ipsum dolor sit amet");
mock.object.doString("Ut enim ad minim veniam");
mock.object.doNumber(999);
 
mock.verifyAll();

When mock behavior is MockBehavior.Strict, every call to .setup() automatically calls .verifiable() behind the scenes, as the default.

let mock = TypeMoq.Mock.ofType(Doer, TypeMoq.MockBehavior.Strict);
 
mock.setup(x => x.doNumber(999)); // Times.once()
mock.setup(x => x.doVoid()).verifiable(Times.atMostOnce());
 
mock.object.doVoid();
mock.object.doNumber(999);
 
mock.verifyAll();
Verify expectation invocation order
Expectation invocation order Description
TypeMoq.ExpectedCallType.InAnyOrder Only call count considered (default value)
TypeMoq.ExpectedCallType.InSequence Both call count and order considered
let mock = Mock.ofInstance((x: number) => { });
 
mock.setup(x => x(1)).verifiable(Times.once(), ExpectedCallType.InSequence);
mock.setup(x => x(2)).verifiable(Times.once(), ExpectedCallType.InSequence);
 
mock.object(2);
mock.object(1);
 
mock.verifyAll();  // it should throw MockException

Create global mocks

Static global mocks

Static global mocks are created by specifying a class type or an existing object, similar to regular static mocks.

You may also specify a container object for the type/object being mocked.

For browsers the top global object is the window object, which is the default container value in TypeMoq.GlobalMock. For node.js the top global object is the global object.

Using class types
// global scope
 
interface IGlobalBar {
  value: string;
}
 
class GlobalBar implements IGlobalBar {
  value: string = '';
}
 
// Create an instance using class as ctor parameter
let mock: TypeMoq.IGlobalMock<GlobalBar> = TypeMoq.GlobalMock.ofType(GlobalBar, global);
 
// Create an instance using class as ctor parameter and casting result to interface
let mock: TypeMoq.IGlobalMock<IGlobalBar> = TypeMoq.GlobalMock.ofType(GlobalBar, global);
 
// Create an instance using interface as type variable and class as ctor parameter
let mock: TypeMoq.IGlobalMock<IGlobalBar> = TypeMoq.GlobalMock.ofType<IGlobalBar>(GlobalBar, global);
 
// Create an instance of 'XmlHttpRequest' global type
let mock = TypeMoq.GlobalMock.ofType(XMLHttpRequest, global);
Using existing objects, including function objects

When creating mock instances out of global objects (such as window.localStorage), you should provide the name of the global object ("localStorage" in this case) as the second parameter.

// Create an instance using class as ctor parameter and ctor args
let bar = new Bar();
let foo = new Foo(bar);
let mock: TypeMoq.IGlobalMock<Foo> = TypeMoq.GlobalMock.ofInstance(foo);
 
// Create an instance using a generic class as ctor parameter and ctor args
let foo = new GenericFoo(Bar);
let mock: TypeMoq.IGlobalMock<GenericFoo<Bar>> = TypeMoq.GlobalMock.ofInstance(foo);
 
// Create an instance from an existing object
let bar = new GlobalBar();
let mock: TypeMoq.IGlobalMock<GlobalBar> = TypeMoq.GlobalMock.ofInstance(bar);
 
// Create an instance from a function object
let mock1: TypeMoq.IGlobalMock<() => string> = TypeMoq.GlobalMock.ofInstance(someGlobalFunc);
let mock2: TypeMoq.IGlobalMock<(a: any, b: any, c: any) => string> = TypeMoq.GlobalMock.ofInstance(someGlobalFuncWithArgs);
 
// Create an instance from 'window.localStorage' global object
let mock = TypeMoq.GlobalMock.ofInstance(localStorage, "localStorage");

Note: Due to browser security limitations, global mocks created by specifying class type cannot have constructor arguments

Dynamic global mocks

Dynamic global mocks are created by specifying a type parameter and the name of the global object as the first constructor argument.

// Create an instance using a class as type parameter
let mock: TypeMoq.IGlobalMock<GlobalBar> = TypeMoq.GlobalMock.ofType2<GlobalBar>("GlobalBar", global);
 
// Create an instance using an interface as type parameter
let mock: TypeMoq.IGlobalMock<IGlobalBar> = TypeMoq.GlobalMock.ofType2<IGlobalBar>("IGlobalBar", global);
 
// Create an instance of 'XmlHttpRequest' global type
let mock = TypeMoq.GlobalMock.ofType2<XMLHttpRequest>("XMLHttpRequest", global);

Compared to static global mocks, dynamic global mocks suffer from the same limitations as regular dynamic mocks.

Auto sandbox global mocks

Replacing and restoring global class types and objects is done automagically by combining global mocks with global scopes.

// global scope
 
function someGlobalFunc() {
  return "someGlobalFunc was called";
}
 
function someGlobalFuncWithArgs(a: any, b: any, c: any) {
  return "someGlobalFuncWithArgs was called";
}
 
// Global no args function is auto sandboxed
let mock = TypeMoq.GlobalMock.ofInstance(someGlobalFunc);
TypeMoq.GlobalScope.using(mock).with(() => {
    someGlobalFunc();
    someGlobalFunc();
});
 
// Global function with args is auto sandboxed
let mock = TypeMoq.GlobalMock.ofInstance(someGlobalFuncWithArgs);
TypeMoq.GlobalScope.using(mock).with(() => {
    someGlobalFuncWithArgs(1,2,3);
    someGlobalFuncWithArgs("1","2","3");
    someGlobalFuncWithArgs(1, 2, 3);
);
 
// Global object is auto sandboxed
let mock = TypeMoq.GlobalMock.ofType(GlobalBar);
TypeMoq.GlobalScope.using(mock).with(() => {
    let bar1 = new GlobalBar();
    bar1.value;
    bar1.value;
});
 
// 'window.XmlHttpRequest' global object is auto sandboxed
let mock = TypeMoq.GlobalMock.ofType(XMLHttpRequest);
TypeMoq.GlobalScope.using(mock).with(() => {
    let xhr1 = new XMLHttpRequest();
    xhr1.open("GET", "http://www.typescriptlang.org", true);
    xhr1.send();
    mock.verify(x => x.send(), TypeMoq.Times.exactly(1));
});
let xhr2 = new XMLHttpRequest();
xhr2.open("GET", "http://www.typescriptlang.org", true);
xhr2.send();
mock.verify(x => x.send(), TypeMoq.Times.exactly(1));
 
// 'window.localStorage' global object is auto sandboxed
let mock = TypeMoq.GlobalMock.ofInstance(localStorage, "localStorage");
mock.setup(x => x.getItem(TypeMoq.It.isAnyString())).returns((key: string) => "[]");
TypeMoq.GlobalScope.using(mock).with(() => {
    expect(localStorage.getItem("xyz")).to.eq("[]");
});
localStorage.setItem("xyz", "Lorem ipsum dolor sit amet");
expect(localStorage.getItem("xyz")).to.eq("Lorem ipsum dolor sit amet");

Note: Inside the scope of a TypeMoq.GlobalScope, when constructing objects from global functions/class types which are being replaced by mocks, the constructor always returns the mocked object (of corresponding type) passed in as argument to the TypeMoq.GlobalScope.using function