Guard the mealybug scores in CI with per-test baselines

MealybugRomTest now asserts each test's diff-pixel count against its
known baseline instead of requiring an exact match: the pixel-perfect
tests (m2_win_en_toggle, m3_obp0_change, m3_scx_low_3_bits) are locked
at 0 and the rest cannot regress silently. The profile joins the CI
workflow; when accuracy work improves a score, the baseline should be
tightened in the same commit.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J1wLWscyUGS7CFwc3CjJR8

Author: trekawek

.github/workflows/maven.yml

@@ -37,6 +37,8 @@ jobs:
       run: mvn -B -pl core test -Ptest-blargg-individual
     - name: dmg-acid2
       run: mvn -B -pl core test -Ptest-dmgacid2
+    - name: Mealybug Tearoom (baseline-guarded)
+      run: mvn -B -pl core test -Ptest-mealybug
 
     # Optional: Uploads the full dependency graph to GitHub to improve the quality of Dependabot alerts this repository can receive
     - name: Update dependency graph

core/src/test/java/eu/rekawek/coffeegb/core/integration/mealybug/MealybugRomTest.java

@@ -1,53 +1,97 @@
 package eu.rekawek.coffeegb.core.integration.mealybug;
 
+import eu.rekawek.coffeegb.core.Gameboy;
 import eu.rekawek.coffeegb.core.GameboyType;
+import eu.rekawek.coffeegb.core.integration.support.ImageTestRunner;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
 
 import java.io.File;
-import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
+import java.util.Map;
 
-import static eu.rekawek.coffeegb.core.integration.support.RomTestUtils.testRomWithImage;
+import static org.junit.Assert.assertTrue;
 
 /**
- * Mealybug Tearoom tests: mid-scanline writes to the PPU registers (SCX/SCY, LCDC bits, BGP)
- * during mode 3. The expected images were captured from real hardware (DMG-CPU B where the
- * revisions differ, DMG-blob otherwise); a test passes when the frame at the LD B,B breakpoint
- * is pixel-identical.
+ * Mealybug Tearoom tests: mid-scanline writes to the PPU registers during mode 3, compared
+ * against photos of a real DMG-CPU B (DMG-blob where no CPU B photo exists). The tests run
+ * with the FAST_FORWARD boot because they reuse the boot ROM's VRAM leftovers (the (r) logo
+ * tile) as sprite data.
+ *
+ * <p>Each ROM asserts that the number of differing pixels does not exceed its known
+ * baseline, so the pixel-exact tests are locked at 0 and the rest cannot regress silently.
+ * When an accuracy change improves a score, tighten the baseline here.
  */
 @RunWith(Parameterized.class)
 public class MealybugRomTest {
 
-    private final Path rom;
+    private static final Map<String, Integer> BASELINES = Map.ofEntries(
+            Map.entry("m2_win_en_toggle.gb", 0),
+            Map.entry("m3_bgp_change.gb", 21),
+            Map.entry("m3_bgp_change_sprites.gb", 20),
+            Map.entry("m3_lcdc_bg_en_change.gb", 11),
+            Map.entry("m3_lcdc_bg_map_change.gb", 192),
+            Map.entry("m3_lcdc_obj_en_change.gb", 2),
+            Map.entry("m3_lcdc_obj_en_change_variant.gb", 54),
+            Map.entry("m3_lcdc_obj_size_change.gb", 360),
+            Map.entry("m3_lcdc_obj_size_change_scx.gb", 230),
+            Map.entry("m3_lcdc_tile_sel_change.gb", 776),
+            Map.entry("m3_lcdc_tile_sel_win_change.gb", 1062),
+            Map.entry("m3_lcdc_win_en_change_multiple.gb", 8316),
+            Map.entry("m3_lcdc_win_en_change_multiple_wx.gb", 15756),
+            Map.entry("m3_lcdc_win_map_change.gb", 212),
+            Map.entry("m3_obp0_change.gb", 0),
+            Map.entry("m3_scx_high_5_bits.gb", 84),
+            Map.entry("m3_scx_low_3_bits.gb", 0),
+            Map.entry("m3_scy_change.gb", 4269),
+            Map.entry("m3_window_timing.gb", 3),
+            Map.entry("m3_window_timing_wx_0.gb", 130),
+            Map.entry("m3_wx_4_change.gb", 229),
+            Map.entry("m3_wx_4_change_sprites.gb", 10),
+            Map.entry("m3_wx_5_change.gb", 638),
+            Map.entry("m3_wx_6_change.gb", 13799));
 
-    public MealybugRomTest(String name, Path rom) {
+    private final File rom;
+
+    private final int baseline;
+
+    public MealybugRomTest(String name, File rom, int baseline) {
         this.rom = rom;
+        this.baseline = baseline;
     }
 
     @Parameterized.Parameters(name = "{0}")
     public static Collection<Object[]> data() {
         File dir = Paths.get("src/test/resources/roms/mealybug").toFile();
-        File[] roms = dir.listFiles((d, n) -> n.endsWith(".gb"));
-        Arrays.sort(roms);
         List<Object[]> params = new ArrayList<>();
-        for (File rom : roms) {
-            // ROMs without an expected image are CGB-only variants
-            if (new File(dir, rom.getName().replace(".gb", ".png")).isFile()) {
-                params.add(new Object[]{rom.getName(), rom.toPath()});
+        for (Map.Entry<String, Integer> e : BASELINES.entrySet()) {
+            File rom = new File(dir, e.getKey());
+            if (rom.isFile()) {
+                params.add(new Object[]{e.getKey(), rom, e.getValue()});
             }
         }
+        params.sort((a, b) -> ((String) a[0]).compareTo((String) b[0]));
         return params;
     }
 
     @Test
     public void test() throws Exception {
-        // FAST_FORWARD: the tests reuse the boot ROM's VRAM leftovers (the (r) logo tile)
-        testRomWithImage(rom, GameboyType.DMG, eu.rekawek.coffeegb.core.Gameboy.BootstrapMode.FAST_FORWARD);
+        ImageTestRunner runner =
+                new ImageTestRunner(rom, GameboyType.DMG, Gameboy.BootstrapMode.FAST_FORWARD);
+        ImageTestRunner.TestResult result = runner.runTest();
+        int[] actual = result.getResultRGB();
+        int[] expected = result.getExpectedRGB();
+        int diff = 0;
+        for (int i = 0; i < expected.length; i++) {
+            if (actual[i] != expected[i]) {
+                diff++;
+            }
+        }
+        assertTrue("diff pixels " + diff + " exceeds the known baseline " + baseline
+                + " - an accuracy regression", diff <= baseline);
     }
 }