Java: Testing Private Methods in JUnit using reflection API Example

Student Class with Private Method:

public class Student {

    private String name;
    private int score;

    public Student(String name, int score) {
        this.name = name;
        this.score = score;
    }

    public String getName() {
        return name;
    }

    public int getScore() {
        return score;
    }

    private String getGrade() { //private method
        if (score >= 90) {
            return "A";
        } else if (score >= 80) {
            return "B";
        } else if (score >= 70) {
            return "C";
        } else if (score >= 50) {
            return "D";
        } else {
            return "E";
        }
    }
}

Junit Test Code:

import org.junit.Test;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import static org.junit.Assert.assertEquals;

public class StudentTest {
    @Test
    public void testGetGrade() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        
       Student student = new Student("Mike Kane", 90);

        // Using reflection to access private method
        Method getGradeMethod = Student.class.getDeclaredMethod("getGrade");
        getGradeMethod.setAccessible(true);

        // Accessing Private getGradeMethod method
        String grade = (String) getGradeMethod.invoke(student);

        // Asserting the result of the private method
        assertEquals("A", grade);
    }
}

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