Tax implements Taxable { public double calcTax(double grossIncome, int dependents) throws IllegalArgumentException{ if (grossIncome <0 ){ throw new IllegalArgumentException("Gross income can't be negative"); } return (grossIncome*0.33 - dependents*100); }  double calcTax(double grossIncome, int dependents); double applyStudentDeduction(double taxAmount, 
    		                                int numOfStudents);  }
@Test public void testZeroTax() { assertEquals("Tax on zero income is not zero", 0, tax.calcTax(0, 0),0 ); }