test: migrate ExecutableRefTest to JUnit 5 (#4518)

src/test/java/spoon/test/executable/ExecutableRefTest.java

@@ -16,7 +16,12 @@
  */
 package spoon.test.executable;
 
-import org.junit.Test;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Method;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
 import spoon.Launcher;
 import spoon.reflect.code.CtAbstractInvocation;
 import spoon.reflect.code.CtBlock;
@@ -37,13 +42,9 @@
 import spoon.test.executable.testclasses.Pozole;
 import spoon.testing.utils.ModelUtils;
 
-import java.lang.reflect.Constructor;
-import java.lang.reflect.Method;
-import java.util.List;
-
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 import static spoon.testing.utils.ModelUtils.build;
 import static spoon.testing.utils.ModelUtils.canBeBuilt;