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fix(jest-mock): spyOn should support 0 key in objects (#14077) #14082

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fix(jest-mock): spyOn should support 0 key in objects (#14077) #14082

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a5e5ac0
spyOn should support zero key in objects (fix #14077)
octaharon Apr 18, 2023
a77fc46
fix(jest-mock): spyOn should support `0` key in objects (#14077)
octaharon Apr 18, 2023
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
- `[jest-mock]` Tweak typings to allow `jest.replaceProperty()` replace methods ([#14008](https://github.com/facebook/jest/pull/14008))
- `[jest-snapshot]` Fix a potential bug when not using prettier and improve performance ([#14036](https://github.com/facebook/jest/pull/14036))
- `[@jest/transform]` Do not instrument `.json` modules ([#14048](https://github.com/facebook/jest/pull/14048))
- `[jest-mock]` Fix `jest.spyOn()` to correctly handle `0` as a method/property name ([#14082](https://github.com/facebook/jest/pull/14082))

### Chore & Maintenance

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22 changes: 22 additions & 0 deletions packages/jest-mock/src/__tests__/index.test.ts
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Expand Up @@ -1308,6 +1308,15 @@ describe('moduleMocker', () => {
expect(() => {
moduleMocker.spyOn(null, 'method');
}).toThrow('spyOn could not find an object to spy on for method');
expect(() => {
moduleMocker.spyOn({} as Record<string, any>, '');
}).toThrow('No property name supplied');
expect(() => {
moduleMocker.spyOn({} as Record<number, any>, NaN);
}).toThrow('No property name supplied');
expect(() => {
moduleMocker.spyOn({}, undefined);
}).toThrow('No property name supplied');
expect(() => {
moduleMocker.spyOn({}, 'method');
}).toThrow(
Comment on lines +1311 to 1322
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In a way these message (and also some of "Cannot spy on the method property because it is not a function" below) are somewhat misleading. How about reworking the whole check logic like this or so:

if (methodKey == null) {
  throw new Error('No property name supplied');
}

if (accessType) {
  return this._spyOnProperty(object, methodKey, accessType);
}

const original = object[methodKey];

if (!original) {
  throw new Error(
    `Property ${String(methodKey)} does not exist in the provided object`,
  );
}

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E.g., spyOn getters or setters has property existence check:

https://github.com/facebook/jest/blob/15af9b3b6f53a4f2f2e39d328eb6ef9f46ba91c4/packages/jest-mock/src/index.ts#L1268-L1270

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@octaharon octaharon Apr 19, 2023 •
edited

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If you ask me, I have no objections. But the messages you refer to were implemented back in 2018 (#5107) for reasons I'm not aware of, and changing those go beyond the scope of fixing the related bug and this PR, I believe. Feel free to do it in a separate PR though, but please note that the code you suggested will not fix the bug and can possibly create more bugs, because methodKey==null is an incorrect way to check for an object key, since it's true only for undefined and null, at least according to MDN

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since it's true for methodKey===0

Not sure I follow this. methodKey == null would exclude only undefined and null, hence the message 'No property name supplied' is correct. This message does not sound correct if user passed '' or NaN as a methodKey. Do I miss something?

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@octaharon octaharon Apr 19, 2023 •
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That message for sure doesn't sound correct, but still it was there for 5 years, and I don't believe I'm in position to decide the way it should be changed.

I personally don't see how null and '' are different in this context, for instance, yet getting a message like that would not help me much if I've passed a variable as the second argument (i.e. "supplied" something), which could possibly be any of the above. If I was to make a statement, I'd say if (!object[methodKey]) is enough to cover all the edge cases here, resulting in the same error, i.e. Method ${methodKey} doesn't exist in the provided object, assuming spyOn expects a function. Also I don't believe testing for particular error strings is a good approach in general, at least when they are literal strings instead of shared constants. The aforementioned tests I've implemented do match the existing behaviour, which was not covered before.

However, I don't mind putting in a few extra lines of code, but if are willing to take the responsibility for those changes, please provide the exact requirements.

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Feel free to do it in a separate PR though

See #14087

Expand All @@ -1320,6 +1329,19 @@ describe('moduleMocker', () => {
);
});

it('should not throw when spying on a method named `0`', () => {
let haveBeenCalled = false;
const obj = {
0: () => {
haveBeenCalled = true;
},
};
const spy = moduleMocker.spyOn(obj, 0);
obj[0].call(null);
expect(haveBeenCalled).toBe(true);
expect(spy).toHaveBeenCalled();
});

it('supports clearing a spy', () => {
let methodOneCalls = 0;
const obj = {
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2 changes: 1 addition & 1 deletion packages/jest-mock/src/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1168,7 +1168,7 @@ export class ModuleMocker {
);
}

if (!methodKey) {
if (!methodKey && !Number.isFinite(methodKey)) {
throw new Error('No property name supplied');
}

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