Require real merge commit and keep level tests embedded

app/src/main/java/solutions/tretter/githugandroid/levels/FindOldBranchLevel.kt

@@ -47,4 +47,13 @@ internal fun findOldBranchLevel(): Level = level(
     testCases = listOf(
         levelTestCase("checkout old branch", "git checkout solve_world_hunger"),
     ),
+    setupChecks = listOf(
+        levelSetupCheck(
+            "upstream branch puzzle shape is present",
+            "find_old_branch should start on master with upstream distractor branches and solve_world_hunger.",
+        ) { repo ->
+            repo.headBranch == "master" &&
+                repo.branches.keys == setOf("blowup_sun_for_ransom", "cure_common_cold", "master", "solve_world_hunger")
+        },
+    ),
 )