elvitin
elvitin
PostsComments
DDeno
Created by elvitin on 1/20/2024 in #help
Strange behavior of the assertRejects() method.
Behavior of the assertRejects() method. assertRejects() fails when a non-stubbed method is called before the stubbed method. Let's look at the following example: 
// main.ts
export class MainClass {
  async mainFn(): Promise<void> {
    await this.foo();
    await this.bar();
  }

  foo(): Promise<string> {
    return Promise.resolve("foo");
  }

  bar(): Promise<string> {
    return Promise.resolve("bar");
  }
}
// main.ts
export class MainClass {
  async mainFn(): Promise<void> {
    await this.foo();
    await this.bar();
  }

  foo(): Promise<string> {
    return Promise.resolve("foo");
  }

  bar(): Promise<string> {
    return Promise.resolve("bar");
  }
}
// main_test.ts
import { describe } from "https://deno.land/std@0.212.0/testing/bdd.ts";
import { stub } from "https://deno.land/std@0.212.0/testing/mock.ts";
import { assertRejects } from "https://deno.land/std@0.212.0/assert/mod.ts";
import { MainClass } from "./main.ts";

describe("unit test", () => {
  const mainObj = new MainClass();
  const barStub = stub(
    mainObj,
    "bar",
    () => new Promise((_, reject) => reject(new Error())),
  );

  assertRejects(() => mainObj.mainFn(), "yeah, bar() rejects with Error");
  barStub.restore();
});
// main_test.ts
import { describe } from "https://deno.land/std@0.212.0/testing/bdd.ts";
import { stub } from "https://deno.land/std@0.212.0/testing/mock.ts";
import { assertRejects } from "https://deno.land/std@0.212.0/assert/mod.ts";
import { MainClass } from "./main.ts";

describe("unit test", () => {
  const mainObj = new MainClass();
  const barStub = stub(
    mainObj,
    "bar",
    () => new Promise((_, reject) => reject(new Error())),
  );

  assertRejects(() => mainObj.mainFn(), "yeah, bar() rejects with Error");
  barStub.restore();
});
execute: deno test output: 
FAILED | 0 passed | 1 failed (0ms)

error: Test failed
FAILED | 0 passed | 1 failed (0ms)

error: Test failed
Note that bar() is stubbed to reject the promise with an error. However, bar() only rejects with an error if foo() is not called: 
// main.ts
export class MainClass {
  async mainFn(): Promise<void> {
    //await this.foo(); // <-- foo() is not called
    await this.bar();
  }
//rest of code...
// main.ts
export class MainClass {
  async mainFn(): Promise<void> {
    //await this.foo(); // <-- foo() is not called
    await this.bar();
  }
//rest of code...
execute: deno test output: 
Check file:///tmp/stdstub/main_test.ts
running 1 test from ./main_test.ts
unit test ... ok (1ms)

ok | 1 passed | 0 failed (4ms)
Check file:///tmp/stdstub/main_test.ts
running 1 test from ./main_test.ts
unit test ... ok (1ms)

ok | 1 passed | 0 failed (4ms)
What am I doing wrong? Is this a bug in the stub() method, or what am I not understanding?
3 replies