[J2KT] Add test reproducing protected method visibility translation bug.

Reproduces problem with `protected` method translated as `public`, and `protected` override which is incorrectly translated as `protected` (should also be `public`).

PiperOrigin-RevId: 926024096

Author: Googler

transpiler/javatests/com/google/j2cl/readable/java/j2kt/VisibilityModifiers.java

@@ -58,6 +58,13 @@ protected void protectedMethod() {}
     private void privateMethod() {}
   }
 
+  // TODO(b/519538678): Uncomment when fixed.
+  // public static class ProtectedOverrideOfVisibilityWarningsSuppressed
+  //     extends VisibilityWarningsSuppressed.Public {
+  //   @Override
+  //   protected void protectedMethod() {}
+  // }
+
   @AutoValue
   abstract static class Value {
     @AutoValue.Builder

transpiler/javatests/com/google/j2cl/readable/java/j2ktnotpassing/VisibilityModifiers.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2026 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package j2ktnotpassing;
+
+public final class VisibilityModifiers {
+  @SuppressWarnings("j2kt:visibility")
+  public static class VisibilityWarningsSuppressed {
+    public static class Public {
+      // This one is translated as public
+      protected void protectedMethod() {}
+    }
+  }
+
+  public static class ProtectedOverrideOfVisibilityWarningsSuppressed
+      extends VisibilityWarningsSuppressed.Public {
+    // TODO(b/519538678): This one is translated as protected, but should be public because it
+    // overrides a public method.
+    @Override
+    protected void protectedMethod() {}
+  }
+}

transpiler/javatests/com/google/j2cl/readable/java/j2ktnotpassing/output_kt/VisibilityModifiers.kt.txt

@@ -0,0 +1,35 @@
+// Generated from "j2ktnotpassing/VisibilityModifiers.java"
+@file:Suppress(
+ "ALWAYS_NULL",
+ "PARAMETER_NAME_CHANGED_ON_OVERRIDE",
+ "SENSELESS_COMPARISON",
+ "UNCHECKED_CAST",
+ "UNNECESSARY_LATEINIT",
+ "UNNECESSARY_NOT_NULL_ASSERTION",
+ "UNREACHABLE_CODE",
+ "UNUSED_ANONYMOUS_PARAMETER",
+ "UNUSED_PARAMETER",
+ "UNUSED_VARIABLE",
+ "USELESS_CAST",
+ "VARIABLE_IN_SINGLETON_WITHOUT_THREAD_LOCAL",
+ "VARIABLE_WITH_REDUNDANT_INITIALIZER",
+ "REDUNDANT_ELSE_IN_WHEN",
+ "ACCIDENTAL_OVERRIDE")
+
+package j2ktnotpassing
+
+import javaemul.lang.*
+import j2ktnotpassing.VisibilityModifiers.VisibilityWarningsSuppressed.Public
+import kotlin.Suppress
+
+class VisibilityModifiers {
+ open class VisibilityWarningsSuppressed {
+  open class Public {
+   open fun protectedMethod() {}
+  }
+ }
+ 
+ open class ProtectedOverrideOfVisibilityWarningsSuppressed: Public() {
+  protected override fun protectedMethod() {}
+ }
+}