review: fix: setVisibility should only be used with private, public or protected

src/main/java/spoon/support/reflect/CtModifierHandler.java

@@ -16,6 +16,7 @@
  */
 package spoon.support.reflect;
 
+import spoon.SpoonException;
 import spoon.reflect.declaration.CtElement;
 import spoon.reflect.declaration.ModifierKind;
 import spoon.reflect.factory.Factory;
@@ -104,6 +105,9 @@ public boolean removeModifier(ModifierKind modifier) {
 	}
 
 	public CtModifierHandler setVisibility(ModifierKind visibility) {
+		if (visibility != ModifierKind.PUBLIC && visibility != ModifierKind.PROTECTED && visibility != ModifierKind.PRIVATE) {
+			throw new SpoonException("setVisibility could only be called with a private, public or protected argument value. Given argument: " + visibility);
+		}
 		if (hasModifier(visibility)) {
 			return this;
 		}

src/test/java/spoon/test/modifiers/TestModifiers.java

@@ -2,15 +2,18 @@
 
 import org.junit.Test;
 import spoon.Launcher;
+import spoon.SpoonException;
 import spoon.reflect.declaration.CtMethod;
 import spoon.reflect.declaration.CtType;
 import spoon.reflect.declaration.ModifierKind;
 import spoon.test.modifiers.testclasses.MethodVarArgs;
+import spoon.test.modifiers.testclasses.StaticMethod;
 
 import java.util.Collections;
 import java.util.Set;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
 
 public class TestModifiers {
 
@@ -33,4 +36,27 @@ public void testMethodWithVarargsDoesNotBecomeTransient() {
         spoon.getEnvironment().setShouldCompile(true);
         spoon.run();
     }
+
+    @Test
+    public void testSetVisibility() {
+        // contract: setVisibility should only work with public/private/protected modifiers
+
+        Launcher spoon = new Launcher();
+        spoon.addInputResource("./src/test/java/spoon/test/modifiers/testclasses/StaticMethod.java");
+        spoon.buildModel();
+
+        CtType<?> myClass = spoon.getFactory().Type().get(StaticMethod.class);
+        CtMethod methodPublicStatic = myClass.getMethodsByName("maMethod").get(0);
+
+        assertEquals(ModifierKind.PUBLIC, methodPublicStatic.getVisibility());
+        methodPublicStatic.setVisibility(ModifierKind.PROTECTED);
+        assertEquals(ModifierKind.PROTECTED, methodPublicStatic.getVisibility());
+        try {
+            methodPublicStatic.setVisibility(ModifierKind.FINAL);
+            fail();
+        } catch (SpoonException e) {
+        }
+
+        assertEquals(ModifierKind.PROTECTED, methodPublicStatic.getVisibility());
+    }
 }

src/test/java/spoon/test/modifiers/testclasses/StaticMethod.java

@@ -0,0 +1,11 @@
+package spoon.test.modifiers.testclasses;
+
+public class StaticMethod {
+    public static int maMethod() {
+        return 42;
+    }
+
+    private static int anotherMethod() {
+        return 42;
+    }
+}