Jess182•4mo ago

Incorrect documentation example (partial mocking)

Hi, I'm trying to replicate the example in the partial mocking documentation, but the test fails because it doesn't override the implementation. VSCode also detects that the spy() function should only receive two arguments. How can i fix or do partial mocking? Thanks - jsr:@std/testing/mock 1.0.12 - deno 2.3.1 - linux mint 22.1 ref: https://docs.deno.com/examples/mocking_tutorial/#partial-mocking

Deno

Testing in isolation with mocks

Master the art of mocking in your unit tests. Learn how spies, stubs, fake time, and other Deno tools let you improve your code and confidence

6 Replies

Jess182OP•4mo ago

I'm still stuck, do you know how I could do partial mocking?

kt3k•3mo ago

Sorry for the confusion. The above example looks wrong to me. If you need to replace the implementation of method, you need to use stub function from @std/testing/mock:

import { assertEquals } from "jsr:@std/assert";
import { assertSpyCall, assertSpyCalls, stub } from "jsr:@std/testing/mock";

class UserService {
  async getUser(id: string) {
    // Complex database query
    return { id, name: "Database User" };
  }

  async formatUser(user: { id: string; name: string }) {
    return {
      ...user,
      displayName: user.name.toUpperCase(),
    };
  }

  async getUserFormatted(id: string) {
    const user = await this.getUser(id);
    return this.formatUser(user);
  }
}

Deno.test("partial mocking with spies", async () => {
  const service = new UserService();

  // Only mock the getUser method
  const getUserSpy = stub(
    service,
    "getUser",
    () => Promise.resolve({ id: "test-id", name: "Mocked User" }),
  );

  try {
    // The formatUser method will still use the real implementation
    const result = await service.getUserFormatted("test-id");

    assertEquals(result, {
      id: "test-id",
      name: "Mocked User",
      displayName: "MOCKED USER",
    });

    // Verify getUser was called with the right arguments
    assertSpyCalls(getUserSpy, 1);
    assertSpyCall(getUserSpy, 0, {
      args: ["test-id"],
    });
  } finally {
    getUserSpy.restore();
  }
});

import { assertEquals } from "jsr:@std/assert";
import { assertSpyCall, assertSpyCalls, stub } from "jsr:@std/testing/mock";

class UserService {
  async getUser(id: string) {
    // Complex database query
    return { id, name: "Database User" };
  }

  async formatUser(user: { id: string; name: string }) {
    return {
      ...user,
      displayName: user.name.toUpperCase(),
    };
  }

  async getUserFormatted(id: string) {
    const user = await this.getUser(id);
    return this.formatUser(user);
  }
}

Deno.test("partial mocking with spies", async () => {
  const service = new UserService();

  // Only mock the getUser method
  const getUserSpy = stub(
    service,
    "getUser",
    () => Promise.resolve({ id: "test-id", name: "Mocked User" }),
  );

  try {
    // The formatUser method will still use the real implementation
    const result = await service.getUserFormatted("test-id");

    assertEquals(result, {
      id: "test-id",
      name: "Mocked User",
      displayName: "MOCKED USER",
    });

    // Verify getUser was called with the right arguments
    assertSpyCalls(getUserSpy, 1);
    assertSpyCall(getUserSpy, 0, {
      args: ["test-id"],
    });
  } finally {
    getUserSpy.restore();
  }
});

kt3k•3mo ago

See also the docs in JSR https://jsr.io/@std/testing/doc/mock

JSR

mock - @std/testing - JSR

@std/testing on JSR: Tools for testing Deno code like snapshot testing, bdd testing, and time mocking

kt3k•3mo ago

I'm trying to fix the docs above https://github.com/denoland/docs/pull/1766

GitHub

fix some mock tutorial examples by kt3k · Pull Request #1766 · de...

This PR fixes 2 examples in examples/mocking_tutorial page.

Jess182OP•3mo ago

Thanks @kt3k for the clarification, is there any plan for the 'spy()' function to replace the implementations?

KyleJune•3mo ago

Spy is just for observing without replacing the original. Stub is for observing and replacing the original. Stub is an extension of Spy. All the assertSpy functions work with stubs. If spy could replace the original function there would be no difference between spy and stub.

Incorrect documentation example (partial mocking)

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