Snapshot tests fail with --coverage due to Istanbul instrumentation.

[brianmcallister]

Not 100% sure if this is an issue with this project, but it appears as though when I run Jest with --coverage, Istanbul instrumentation ends up in the compiled code, which fails my snapshot tests. Here's a look at the Jest output:

  ● LoginPageComponent › should render and match snapshot

    expect(value).toMatchSnapshot()
    
    Received value does not match stored snapshot 1.
    
    - Snapshot
    + Received
    
    @@ -29,12 +29,11 @@
              >
                
            
                <app-input
                  label="Username"
    -             ng-reflect-change="function (value) {
    -              "
    +             ng-reflect-change="function (value) {/* istanbul "
                  ng-reflect-label="Username"
                >
                  <div
                    class="input"
                  >

I found this issue in the Jest repository, and it seems related, though the person reporting the issue was using a different set of libraries, and it looks like he was testing a React application.

Let me know if there's more information I can provide.

[thymikee]

Uh oh. maybe we should remove the ng-reflect-change entirely? Don't think it's super necessary to snapshot this.

[brianmcallister]

I'm a bit new to Angular, but it seems like it's something that you would want, because then the function that you've passed your handler to ends up in the snapshot. I am testing that the functionality works in a separate unit test, but I think there might be some value in "testing" that you've passed the correct props to the correct components.

Again though, very new to Angular so I might be off base there.

[thymikee]

To me function (value) {/* istanbul doesn't reflect any value, but I may be wrong. I'm not currently using Angular, so it's hard for me to tell. It may be helpful, but definitely not in this form. We could improve the snapshot serializer to change this into some kind of token, because we don't want the function implementation written to the disk, right?

For now, I'm cool with accepting a PR which filters out any valid /* istanbul calls like this.

[brianmcallister]

Good point about not needing the function implementation, I definitely agree with that (especially since I unit test those anyway). Maybe something like ng-reflect-change=[Function]... something along those lines.

What would be the correct place to implement a filter like that? Seems like AngularSnapshotSerializer.js, though it seems likely that Istanbul adds those comments after the component gets serialized.

[thymikee]

That's a right place to add this. Something similar was implemented in pretty-format which formats this code inside Jest serializers, so you can check st the implementation there if you like :)

[brianmcallister]

OK, sounds great, thanks. I'll try and carve out some time in the next week or two to work through this.

[thymikee]

Awesome, thank you ❤️

[thymikee]

@brianmcallister have tried this? jestjs/jest#1740 (comment)

[brianmcallister]

Unfortunately, it looks like the betas aren't working at all (at least for me), instead, they just throw errors on every test.

I did dig into this a bit, and this looks like an issue with pretty-format instead of this repository. Although pretty-format does support plugins (which is probably the cleanest way to handle this, maybe?), I don't see an easy way to add a plugin when adding a custom snapshot serializer.

I don't think it makes too much sense to attempt to patch pretty-format here since I think this issue might be specific to Angular.

I'll keep trying the jest betas as they're published and see if that helps.

[thymikee]

When the next beta is up (something above 21.3.0-beta.4), add "testEnvironment": "jsdom" to your Jest config and it should work. Or add setup/teardown methods to current testEnvironment.js (by modifying node_modules or linking the preset) if you want to test it now.

[sylvainleduby]

Same issue here with [email protected] and [email protected] (and [email protected]):

                ng-reflect-resolve-title-component="function (type) {
    -           retu"
    +           /* i"

"Resolved" by increasing the length of the parameter of our function to eventType to move Istanbul's comment out of the string used in the snapshot. But it does not seem robust at all.
Any better (real) solution?

[ahnpnl]

Please try with 7.1.1, the preset now has new serializers to strip out some unnecessary things from snapshot. Feel free to report if you encounter new issues.