[Java] How to set when The constructor Empty () is not visible occurs in junit

1 minute read

Summary of this article

I had a little trouble when using junit with eclipse, so I will describe the setting method as a memorandum.
Specifically, the following error may occur when the test target class has a private constructor, so the workaround is described.

　 The constructor Empty() is not visible

reference

How to test private methods in Junit

[Get method, execute method with Java reflection API]
(http://pppurple.hatenablog.com/entry/2016/07/23/205446)

environment

OS:Windows8.1 32bit
eclipse:4.5.2

Tested class

TestTarget.java



packege com.web.test

public class TestTarget {

  private TestTarget() {
    //No description
  }

  private int minus(int x, int y) {
        return (x - y);
  }

}

junit test class

Create a junit test class for the class under test

SampleTest.java



import static org.junit.Assert.*;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import org.junit.Test;

public class SampleTest {

    @Test
    public void test()
        throws NoSuchMethodException,
        SecurityException,
        IllegalAccessException,
        IllegalArgumentException,
        InvocationTargetException
    {
        TestTarget testTarget = new TestTarget();

        Method method = Sample.class.getDeclaredMethod("minus", int.class, int.class);
        method.setAccessible(true);

        int actual = (int)method.invoke(testTarget, 8, 2);

        assertEquals(6, actual);
    }

If you do this
　The constructor Empty() is not visible
Has occurred, so change it as follows

SampleTest.java



import static org.junit.Assert.*;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import org.junit.Test;

public class SampleTest {

    @Test
    public void test()
        throws NoSuchMethodException,
        SecurityException,
        IllegalAccessException,
        IllegalArgumentException,
        InvocationTargetException
    {
        //Before correction
        //TestTarget testTarget = new TestTarget();
　　　　　　　　　　　　　　　　//Revised
　　　　　　　　　　　　　　　　//Get an instance of the class under test using the reflection API
        TestTarget testTarget = Class.forName("com.web.test.TestTarget").newInstance();

        Method method = testTarget.class.getDeclaredMethod("minus", int.class, int.class);
        method.setAccessible(true);

        int actual = (int)method.invoke(testTarget, 8, 2);

        assertEquals(6, actual);
    }

with this
　The constructor Empty() is not visible
Has been resolved

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