NumberExpression extends Expression { @Override public int interpret() { return number; } NumberExpression(int number);  NumberExpression(String s); @Override int interpret(); @Override String toString();  }
@Test public void testFromString() throws Exception { final int expectedValue = getFirst().interpret(); final String testStingValue = String.valueOf(expectedValue); final NumberExpression numberExpression = new NumberExpression(testStingValue); assertEquals(expectedValue, numberExpression.interpret()); }