Don't crash if tests are enumerated before their test cases are evaluated

Author: grynspan

Sources/Testing/EntryPoints/ABIv0/Encoded/ABIv0.EncodedTest.swift

@@ -81,7 +81,7 @@ extension ABIv0 {
         let testIsParameterized = test.isParameterized
         isParameterized = testIsParameterized
         if testIsParameterized {
-          _testCases = test.testCases?.map(EncodedTestCase.init(encoding:))
+          _testCases = test.uncheckedTestCases?.map(EncodedTestCase.init(encoding:))
         }
       }
       name = test.name

Sources/Testing/Test.swift

@@ -128,6 +128,23 @@ public struct Test: Sendable {
     }
   }
 
+  /// Equivalent to ``testCases``, but without requiring that the test cases be
+  /// evaluated first.
+  ///
+  /// Most callers should not use this property and should prefer ``testCases``
+  /// since it will help catch logic errors in the testing library. Use this
+  /// property if you are interested in the test's test cases, but the test has
+  /// not been evaluated by an instance of ``Runner/Plan`` (e.g. if you are
+  /// implementing `swift test list`.)
+  var uncheckedTestCases: (some Sequence<Test.Case>)? {
+    testCasesState.flatMap { testCasesState in
+      if case let .evaluated(testCases) = testCasesState {
+        return testCases
+      }
+      return nil
+    }
+  }
+
   /// Evaluate this test's cases if they have not been evaluated yet.
   ///
   /// The arguments of a test are captured into a closure so they can be lazily