Test

import org.junit.Assert;
import org.junit.Test;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;

public class T11TestSetAge {
    private static final String CLASS_NOT_PRESENT_ERROR_MESSAGE = "Class '%s' not present";
    private static final String METHOD_RETURN_TYPE_ERROR = "Method '%s' in class '%s' should have return type '%s'";
    private static final String WRONG_SALARY_IS_SET = "Wrong salary is set";
    private static final String FIRST_NAME = "firstName";
    private static final String SECOND_NAME = "secondName";
    private static final String NAME_OF_FIELD_AGE = "age";
    private static final int YOUNG_PERSON_AGE = 20;
    private static final int OLD_PERSON_AGE = 40;
    private static final double PERSON_SALARY = 500D;

    private static final String PERSON = "Person";


    private static final String[] methodNames = new String[]{
            "setAge"
    };

    private static final HashMap<String, Class> methodReturnTypes = new HashMap<String, Class>() {{
        put("setAge", void.class);
    }};

    private static final HashMap<String, Class[]> methodParameters = new HashMap<String, Class[]>() {{
        put("setAge", new Class[]{int.class});
    }};


    @Test
    public void test() throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchFieldException {
        assertExistingMethodsAndWorksCorrect(methodNames);
    }

    private void assertExistingMethodsAndWorksCorrect(String[] methodNames) throws NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException, NoSuchFieldException {
        Class cl = getClass(PERSON);
        for (String methodName : methodNames) {
            Method method =
                    methodParameters.get(methodName).length == 0
                            ? cl.getDeclaredMethod(methodName)
                            : cl.getDeclaredMethod(methodName, methodParameters.get(methodName));
            Class<?> returnType = method.getReturnType();
            Assert.assertTrue(
                    String.format(METHOD_RETURN_TYPE_ERROR,
                            methodName,
                            PERSON,
                            methodReturnTypes.get(methodName)),
                    returnType.equals(methodReturnTypes.get(methodName)));

            Assert.assertTrue(WRONG_SALARY_IS_SET,
                    assertSetAgeCorrect(method, cl));
        }
    }

    private boolean assertSetAgeCorrect(Method method, Class cl) throws InvocationTargetException, NoSuchMethodException, InstantiationException, IllegalAccessException, NoSuchFieldException {
        return correctSetAge(method, cl)
                && correctSetAgeWithZERO(method, cl);
    }

    private boolean correctSetAgeWithZERO(Method setAge, Class cl) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchFieldException {
        Constructor constructor = cl.getDeclaredConstructor(String.class,
                String.class, int.class, double.class);
        constructor.setAccessible(true);
        Object person = constructor.newInstance(FIRST_NAME, SECOND_NAME,
                OLD_PERSON_AGE, PERSON_SALARY);

        boolean error = false;
        try {
            setAge.invoke(person, 0);
        } catch (InvocationTargetException ite) {
            error = true;
        }

        return error;
    }

    private boolean correctSetAge(Method setAge, Class cl) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchFieldException {

        Constructor constructor = cl.getDeclaredConstructor(String.class,
                String.class, int.class, double.class);
        constructor.setAccessible(true);
        Object person = constructor.newInstance(FIRST_NAME, SECOND_NAME,
                YOUNG_PERSON_AGE, PERSON_SALARY);

        setAge.invoke(person, YOUNG_PERSON_AGE);

        Field fieldAge = person.getClass().getDeclaredField(NAME_OF_FIELD_AGE);
        fieldAge.setAccessible(true);
        int age = (int) fieldAge.get(person);

        return YOUNG_PERSON_AGE == age;
    }

    private Class getClass(String className) {
        Assert.assertTrue(String.format(CLASS_NOT_PRESENT_ERROR_MESSAGE, className),
                Classes.allClasses.containsKey(className));
        return Classes.allClasses.get(className);
    }
}