Jest: toEqual ignores keys with undefined properties

[321ckatz123]

If a property is undefined, Jest appears to ignore it when calling .toEqual().

import _ from "lodash"; describe("test", () => { it("returns an object with the correct nodes", () => { let a = {"key1": undefined, "key2": "a"}; let b = {"key2": "a"}; expect(a).toEqual(b); expect(_.isEqual(a, b)).toBeFalsy(); }); });

This simple test will pass. As you can see by adding lodash, it should be false.

My output:
Using Jest CLI v0.8.2, jasmine1
Running 1 test suite...
PASS processors\hockey__tests__\events.js (0.573s)
1 test passed (1 total in 1 test suite, run time 1.076s)
----------|----------|----------|----------|----------|----------------|
File | % Stmts | % Branch | % Funcs | % Lines |Uncovered Lines |
----------|----------|----------|----------|----------|----------------|
----------|----------|----------|----------|----------|----------------|
All files | 100 | 100 | 100 | 100 | |
----------|----------|----------|----------|----------|----------------|

[jamedranoa]

this is coming from here. @cpojer is there a reason why that check can't be removed? all the tests on the jest repository pass without it.

[cpojer]

@jamedranoa yes, I plan on eventually removing this check. Unfortunately we have a shitload of tests at FB that depend on this behavior. My goal is to unfork jasmine eventually though, it'll happen in the next few months.

[jamedranoa]

Cool thank you! :+1:

[scsper]

@cpojer Are there still plans to remove this?

[aaronabramov]

@scsper we still have plans, but there's still too many FB tests that depend on this behavior, so it's not going to happen soon :/

[peter-leonov]

Hey guys, what about adding a feature switch for us open source users to use isEqual() without strange JSON.stringify() related surprises?

[mnpenner]

Is there a workaround for this?

[JasonCust]

@cpojer any updates on this issue? I ran into it recently and noticed this issue has gone stale.

[SimenB]

You can create your own matcher using lodash.toEqual if you want

[JasonCust]

@SimenB For now I have a couple workarounds (e.g. using toHaveProperty) but I was hoping there was some timeline on a fix or at the least a note in the docs about this issue.

[lukescott]

Hmmm... the issue says it ignores undefined. I'm seeing the opposite - it does not ignore undefined properties. It seems to depend on which side goes into expect() and vs toEqual().

Wish there was a way to toggle the behavior. In my case I want it to ignore undefined as JSON.stringify will strip undefined properties anyway (so I don't care).

[phamj88]

@lukescott
what did your test case case look like?
Im seeing undefined gets ignored no matter which side the toEquals it is in.

[mike1808]

Is anyone concerned with this? I got a bug today because of this issue.

[SimenB]

This is sorta fixed, we have toStrictEqual now.

EDIT: based on this comment, I'll call this issue fixed:

would be impossible to roll out at FB. Having a separate strict matcher in Jest is the better option.

Slightly a footgun that's it's not the default, but legacy.

If you want to enforce usage in your code base, you can use https://github.com/jest-community/eslint-plugin-jest/pull/134, which can autofix your code

[glasser]

It might help if the docs for toEqual mentioned the ways in which it differs from toStrictEqual instead of you having to discover toStrictEqual on your own.