How to wrap a catch for InvocationTargetException in a junit test - https://compsci.rocks/invocationtargetexception-fix/

testMethod.java

public void test_MeetAtMidnight() throws Exception {
  RouteCipher rc = new RouteCipher( 3, 5 );
  setField( rc, "numRows", 3 );
  setField( rc, "numCols", 5 );
  Method m = RouteCipher.class.getDeclaredMethod( "fillBlock", new Class[]{ String.class } );
  m.setAccessible( true );

  // This is the problem line
  m.invoke( rc, "Meet at midnight" );

  String[][] exp = { { "M", "e", "e", "t", " " }, { "a", "t", " ", "m", "i" }, { "d", "n", "i", "g", "h" } };
  String[][] act = getField( rc, "letterBlock" );

  assertArrayEquals( "fillBlock failed", exp, act );
}

testMethod_fixed.java

public void test_MeetAtMidnight() throws Exception {
  RouteCipher rc = new RouteCipher( 3, 5 );
  setField( rc, "numRows", 3 );
  setField( rc, "numCols", 5 );
  Method m = RouteCipher.class.getDeclaredMethod( "fillBlock", new Class[]{ String.class } );
  m.setAccessible( true );
  try {
    m.invoke( rc, "Meet at midnight" );
  } catch ( InvocationTargetException e ) {
    throw (Exception) e.getCause();
  }
  String[][] exp = { { "M", "e", "e", "t", " " }, { "a", "t", " ", "m", "i" }, { "d", "n", "i", "g", "h" } };
  String[][] act = getField( rc, "letterBlock" );

  assertArrayEquals( "fillBlock failed", exp, act );
}