test: move Roborazzi results into subfolders

Previously all `_actual.png` and `_compare.png` were in the root of the
Roborazzi output folder, which risked conflicts between different
*Test.kt output screenshots.

`Anki-Android/AnkiDroid/build/outputs/roborazzi`

Moving these files into `/StudyScreenScreenshotTest` meant that correct
and incorrect baselines were located in the same folder, which added
noise to the comparison

Structure:

```
roborazzi/StudyScreenScreenshotTest/
  Phone_BOX_false.png
  Phone_BOX_true.png
  Tablet_BOX_false.png
  diffs/ # one file from the root is copied, along with diagnostics
    Phone_BOX_false.png
    Phone_BOX_false_actual.png
    Phone_BOX_false_compare.png
```

Requested:
https://redirect.github
.com/ankidroid/pull/20943#pullrequestreview-4224241914

Somewhat related to 20942

Assisted-by: Claude Opus 4.7 - diagnostics, some implementation

Author: david-allison

AnkiDroid/src/test/java/com/ichi2/anki/ScreenshotTest.kt

@@ -15,8 +15,13 @@
  */
 package com.ichi2.anki
 
+import com.github.takahirom.roborazzi.ExperimentalRoborazziApi
+import com.github.takahirom.roborazzi.RoborazziOptions
+import com.github.takahirom.roborazzi.captureScreenRoboImage
+import com.github.takahirom.roborazzi.provideRoborazziContext
 import org.junit.experimental.categories.Category
 import org.robolectric.annotation.GraphicsMode
+import java.io.File
 
 interface ScreenshotTestCategory
 
@@ -25,4 +30,36 @@ interface ScreenshotTestCategory
  */
 @Category(ScreenshotTestCategory::class)
 @GraphicsMode(GraphicsMode.Mode.NATIVE)
-abstract class ScreenshotTest : RobolectricTest()
+abstract class ScreenshotTest : RobolectricTest() {
+    /**
+     * Captures a screenshot to `build/outputs/roborazzi/<TestClass>/<name>.png`.
+     *
+     * Writes to /diffs/ if there is an issue.
+     */
+    @OptIn(ExperimentalRoborazziApi::class)
+    protected fun captureScreen(name: String) {
+        // Note: this.javaClass should not be used inside a lambda, as 'this' will be unnamed
+        val classDir = "build/outputs/roborazzi/${this.javaClass.simpleName}"
+        val diffDir = File("$classDir/diffs")
+        // baseline is always in the root for the class, copied to /diffs/ if a change occurred
+        val baseline = File("$classDir/$name.png")
+        captureScreenRoboImage(
+            filePath = baseline.path,
+            roborazziOptions = provideRoborazziContext().options.withCompareOutputDir(diffDir.path),
+        )
+
+        // copy the baseline into /diffs (if it exists)
+        // /diffs/ is used so 'clean' baselines are not mixed with diffs to inspect
+        val diffWritten =
+            File(diffDir, "${name}_compare.png").exists() ||
+                File(diffDir, "${name}_actual.png").exists()
+        if (diffWritten && baseline.isFile) {
+            baseline.copyTo(File(diffDir, baseline.name), overwrite = true)
+        }
+    }
+}
+
+/** Sets the directory for _actual.png and _compare.png */
+@OptIn(ExperimentalRoborazziApi::class)
+private fun RoborazziOptions.withCompareOutputDir(dir: String): RoborazziOptions =
+    copy(compareOptions = compareOptions.copy(outputDirectoryPath = dir))

AnkiDroid/src/test/java/com/ichi2/anki/ui/windows/reviewer/StudyScreenScreenshotTest.kt

@@ -16,8 +16,6 @@
 package com.ichi2.anki.ui.windows.reviewer
 
 import androidx.test.core.app.ActivityScenario
-import com.github.takahirom.roborazzi.ExperimentalRoborazziApi
-import com.github.takahirom.roborazzi.captureScreenRoboImage
 import com.ichi2.anki.ScreenshotTest
 import com.ichi2.anki.previewer.CardViewerActivity
 import com.ichi2.anki.settings.Prefs
@@ -40,15 +38,14 @@ class StudyScreenScreenshotTest(
         RuntimeEnvironment.setQualifiers(config.qualifier.toString())
     }
 
-    @OptIn(ExperimentalRoborazziApi::class)
     @Test
     fun captureScreenshot() {
         ActivityScenario
             .launch<CardViewerActivity>(
                 ReviewerFragment.getIntent(targetContext),
             ).use { scenario ->
                 scenario.onActivity {
-                    captureScreenRoboImage(filePath = "build/outputs/roborazzi/${this.javaClass.simpleName}/$config.png")
+                    captureScreen(config.toString())
                 }
             }
     }

tools/compare-screenshot-test.sh

@@ -154,9 +154,11 @@ gradle_quiet "${REPO_ROOT}/gradlew" -p "$REPO_ROOT" \
     ${GRADLE_TESTS_ARG[@]+"${GRADLE_TESTS_ARG[@]}"}
 
 
-shopt -s nullglob
-diffs=("${OUT_DIR}"/*_compare.png)
-shopt -u nullglob
+# Recurse — Roborazzi writes *_compare.png inside directories
+diffs=()
+while IFS= read -r line; do
+    diffs+=("$line")
+done < <(find "$OUT_DIR" -type f -name '*_compare.png')
 
 if [ ${#diffs[@]} -eq 0 ]; then
     label="${TEST_FILTER:-all screenshot tests}"