How to mock modules like you can with jest?

With node/jest I was able to mock specific functions from modules using

jest.mock

jest.mock

at the start of the test file. How can I do this in Deno? I have a module which calls a function from another module:

import {foo} from "foo";

export function bar(a: number): number {
  return foo(a * 2);
}

import {foo} from "foo";

export function bar(a: number): number {
  return foo(a * 2);
}

How can I substitute

foo

foo

with a mock/stub/fake for the scope of a test file?

jest.mock("foo", () => ({
  foo: jest.fn();
}));

import {foo} from "foo";

describe("example", () => {
  it("returns the expected number", () => {
    foo.mockImplementation((_) => 100);
    ...

jest.mock("foo", () => ({
  foo: jest.fn();
}));

import {foo} from "foo";

describe("example", () => {
  it("returns the expected number", () => {
    foo.mockImplementation((_) => 100);
    ...

Deno•2y ago•

8 replies

numberkruncher

How to mock modules like you can with jest?

With node/jest I was able to mock specific functions from modules using

jest.mock

jest.mock

at the start of the test file. How can I do this in Deno? I have a module which calls a function from another module:

import {foo} from "foo";

export function bar(a: number): number {
  return foo(a * 2);
}

import {foo} from "foo";

export function bar(a: number): number {
  return foo(a * 2);
}

How can I substitute

foo

foo

with a mock/stub/fake for the scope of a test file?

jest.mock("foo", () => ({
  foo: jest.fn();
}));

import {foo} from "foo";

describe("example", () => {
  it("returns the expected number", () => {
    foo.mockImplementation((_) => 100);
    ...

jest.mock("foo", () => ({
  foo: jest.fn();
}));

import {foo} from "foo";

describe("example", () => {
  it("returns the expected number", () => {
    foo.mockImplementation((_) => 100);
    ...

How to mock modules like you can with jest?

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