Mocha: TypeError: Cannot read property 'equal' of undefined

[frankli-dev]

Prerequisites

• [x] Checked that your issue hasn't already been filed by cross-referencing issues with the faq label
• [x] Checked next-gen ES issues and syntax problems by using the same environment and/or transpiler configuration without Mocha to ensure it isn't just a feature that actually isn't supported in the environment in question or a bug in your code.
• [x] 'Smoke tested' the code to be tested by running it outside the real test suite to get a better sense of whether the problem is in the code under test, your usage of Mocha, or Mocha itself
• [x] Ensured that there is no discrepancy between the locally and globally installed versions of Mocha. You can find them with: node node_modules/.bin/mocha --version(Local) and mocha --version(Global). We recommend that you _not_ install Mocha globally.

Description

describe("Array", () => {
  describe("#indexOf()", () => {
    it("shold return -1 when the value is not present", () => {
      [1, 2, 3].indexOf(5).to.equal(-1);
      [1, 2, 3].indexOf(2).to.equal(-1);
    });
  });
});

Steps to Reproduce

I followed the mocha getting started guide

• npm init
• update scripts to "test": "mocha" in package.json file
• yarn add mocha
• make test.js
• add the above code
• yarn test
  

Expected behavior: [What you expect to happen]
I think it should run without an error
Actual behavior: [What actually happens]
it displays the following:

1) Array
       #indexOf()
         shold return -1 when the value is not present:
     TypeError: Cannot read property 'equal' of undefined
      at Context.<anonymous> (test.js:8:16)
      at processImmediate (internal/timers.js:456:21)

Reproduces how often: [What percentage of the time does it reproduce?]

Versions

• The output of mocha --version and node node_modules/.bin/mocha --version: 8.1.1
• The output of node --version: v12.18.1
• Your operating system
  
  
  
  • name and version: macOS High Sierra 10.13.6
  
  
  • architecture (32 or 64-bit): 64
  
  
• Your shell (e.g., bash, zsh, PowerShell, cmd): bash
• Your browser and version (if running browser tests): It's not a browser test
• Any third-party Mocha-related modules (and their versions): nothing
• Any code transpiler (e.g., TypeScript, CoffeeScript, Babel) being used (and its version): nothing

Additional Information

This code is on the mochajs.org page 'Synchronous Code'

[rgroothuijsen]

Assuming you're using Chai, it appears you forgot to wrap your actual value in expect().

[frankli-dev]

Thanks for your answer. But I don't use Chai. I just followed the instructions on getting started page of mocha.
I just installed mocha.

[rgroothuijsen]

That would explain it. Mocha is only a test runner rather than an assertion framework, so you'll have to add those separately if you want to use them.

[frankli-dev]

Cool. Thak makes sense. Then the getting started page of mocha should comment about that in this section, I think.

[frankli-dev]

https://mochajs.org/#synchronous-code

[MoonSupport]

Even in my experience, it was difficult for me to first understand exactly what mocha does too.
I think it would be nice if it was added more clearly to the documentation.