Implement generateRobolectricPreviewTests prototype

[takahirom]

#415

[sergio-sastre]

just as idea. One could provide default versions for roborazzi, robolectric & composablePreviewScaner, but allow to configure them via gradle plugin property

roborazzi {
  automaticPreviewScreenshots {
     ...
     roborazziComposeVersion = "1.20.0
     robolectricVersion = "1.14.2"
     composablePreviewScannerVersion = "0.1.2"
     ...
  }
}

or

roborazzi {
  automaticPreviewScreenshots {
     ...
     libVersions {
        roborazziCompose = "1.20.0
        robolectric = "1.14.2"
        composablePreviewScanner = "0.1.2"
     }
     ...
  }
}

That way it is more independent of external libraries, and convenient in cases were new versions break something that was previously working.

On the other hand, the main disadvantage is that if the public apis of any of those libraries changes the public apis, the generated code will not compile. However, One could throw a meaningful and verbose exception if the versions it is incompatible with are known.

[takahirom]

Thanks. I've incorporated this suggestion.

[sergio-sastre]

I was thinking about this "sdk", which would be the equivalent to the @Preview(apiLevel = X), where the default apiLevel is -1.

Maybe not for the first version, but I believe it would make sense to create one test class for every api level:

val apiLevel = X // if X == -1, default to 34 for example
val previews  = AndroidComposablePreviewScanner()
   .filterPreviews(previewInfo -> info.apiLevel == X)
   .getPreviews()
   
// WARNING: Do not create test if the list if empty, because ParameterizedTest with no parameters throw exceptions
 if ( previews.size > 0 ){
    // here the code to create a test for the previews for apilevel, with @Config(sdk = [apiLevel])
 }

[sergio-sastre]

Idea: For an upcoming version, one could create an annotation @RoborazziConfig with all the desired Roborazzi configs (e.g. tolerance and accessibility) that would map accordingly to a RoborazziOptions.
https://github.com/sergio-sastre/ComposablePreviewScanner#roborazzi

The main thing is, that @RoborazziConfigshould be better in a different module, because it has to be used in the previews in "main", so added via implementation instead of testImplementation, for instance ->

implementation "io.github.takahirom.roborazzi:roborazzi-annotations"

[takahirom]

I am also considering creating a module that might include a RoborazziOptionsMapper. It could be included in an upcoming version.

[sergio-sastre]

Not sure whether enabledis necessary. I'd assume, that if automaticPreviewScreenshots is added, it is enabled, and disabled if not.

What I'm not sure is what would happen with the generated test if automaticPreviewScreenshots is removed? It should be deleted I'd expect?

[takahirom]

Well, in my experience, Gradle plugins are likely to have an 'enable' property, which can be intuitive for users. It would be simpler without the 'enable' property, but this could lead to mistakes in the build logic or elsewhere. I don't have a strong opinion about this.

[sergio-sastre]

right now, the previewInfo parameters like fontScale, locale, etc. are not set.

I've showcased how to set them here which is applied in this test :)

Still some important missing, like "device", and others like "wallpapers" are not currently possible in Robolectric as far as I know... likely worth documenting

[yschimke]

Nice!

[yschimke]

Looks great!

[github-actions]

Snapshot diff report

File name	Image
PreviewWithPropertie s.Preview_Name_Previ ew_Group_API_LEVEL_3 0_W320dp_H640dp_ja_J P_FONT_1_5f_WITH_SYS TEM_UI_WITH_BACKGROU ND_BG_COLOR_42781903 35_NIGHT_NEXUS_5_WAL LPAPER_GREEN_DOMINAT ED_compare.png
Preview2_compare.png

[takahirom]

I don't think it is needed for the first release, but there might be a feature request to adjust the tolerance of the diff.

[sergio-sastre]

Keep in mind that the property name is different before Robolectric 4.12.1

[yschimke]

Rather than supporting older versions, maybe we should warn if using legacy versions? Are there typically reasons not to update robolectric if some new library you introduce uses it?

[takahirom]

Thanks. I added a little comment for it.
a7984d0

[sergio-sastre]

So my understanding is, that for the first version, we do not handle the preview properties, am I right?
I mean, locale, uiMode, fontscale, etc... they are indeed easy to support:
https://github.com/sergio-sastre/Android-screenshot-testing-playground/blob/master/lazycolumnscreen-previews/roborazzi/src/test/java/snapshot/testing/lazycolumn_previews/roborazzi/utils/RobolectricPreviewInfosApplier.kt

and then when creating the test, it has to be called before captureRoboImage, for instance:

    @GraphicsMode(NATIVE)
    @Config(sdk = [34])
    @Test
    fun snapshot() {
        RobolectricPreviewInfosApplier.applyFor(preview)

        captureRoboImage(
            filePath = filePath(AndroidPreviewScreenshotIdBuilder(preview).build())
        ) {
            preview()
        }
    }

Other more complicated, like apiLevel, device etc. can be supported in next versions. Just my opinion.

@takahirom @yschimke
What do you think?

In that case, I'd also document which preview parameters are supported

[takahirom]

@sergio-sastre @yschimke
Thank you for all your reviews!
I've created a new PR to handle the preview settings. Could you please take a look
https://github.com/takahirom/roborazzi/pull/427/files