### Question:
TrigonometricFunctionUtils { public static double atan(double x) { return Math.atan(x); } private  TrigonometricFunctionUtils(); static double acos(double x); static ComplexNumber acos(ComplexNumber z); static double acosh(double x); static ComplexNumber acosh(ComplexNumber z); static double asin(double x); static ComplexNumber asin(ComplexNumber z); static double asinh(double x); static ComplexNumber asinh(ComplexNumber z); static double atan(double x); static ComplexNumber atan(ComplexNumber z); static double atanh(double x); static ComplexNumber atanh(ComplexNumber z); static double cos(double x); static ComplexNumber cos(ComplexNumber z); static double cosh(double x); static ComplexNumber cosh(ComplexNumber z); static double sin(double x); static ComplexNumber sin(ComplexNumber z); static double sinh(double x); static ComplexNumber sinh(ComplexNumber z); static double tan(double x); static ComplexNumber tan(ComplexNumber z); static double tanh(double x); static ComplexNumber tanh(ComplexNumber z);  }### Answer:
@Test public void testNull5() { assertThatIllegalArgumentException() .isThrownBy(() -> TrigonometricFunctionUtils.atan(null)); }