Require real merge commit and keep level tests embedded

app/src/main/java/solutions/tretter/githugandroid/GameModels.kt

@@ -18,6 +18,7 @@ data class CommitNode(
     val id: String,
     val message: String,
     val authorTimestampSeconds: Long? = null,
+    val parentCount: Int = 0,
 )
 
 data class InteractiveAddSession(
@@ -57,6 +58,8 @@ data class Level(
     val setup: () -> RepoState,
     val nativeSetup: (NativeLevelSetup.() -> Boolean)? = null,
     val testCases: List<LevelTestCase> = emptyList(),
+    val negativeTestCases: List<LevelTestCase> = emptyList(),
+    val setupChecks: List<LevelSetupCheck> = emptyList(),
 )
 
 data class LevelTestCase(
@@ -64,4 +67,10 @@ data class LevelTestCase(
     val commands: List<String>,
 )
 
+data class LevelSetupCheck(
+    val name: String,
+    val failureMessage: String,
+    val predicate: (RepoState) -> Boolean,
+)
+
 fun sampleLevels(): List<Level> = allGithugLevels()