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Set of utility classes (with associated unit tests) used by other znerd.org-projects
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// See the COPYRIGHT file for copyright and license information
package org.znerd.util.test;

import java.lang.reflect.Constructor;
import java.lang.reflect.Modifier;

import org.znerd.util.ArrayUtils;
import org.znerd.util.text.TextUtils;

public class TestUtils {

    /**
     * Tests if the specified utility class has a matching constructor. The following is checked:
     * 
     * There must be exactly 1 constructor.
     * 
This constructor must be marked private.
     * 
Invoking the constructor should not throw any exception.
     * 

     * 
     * @param clazz The class to check, should not be null.
     * @throws IllegalArgumentException if clazz == null.
     * @throws TestFailedException In case an issue is found.
     */
    public static final void testUtilityClassConstructor(Class clazz) throws IllegalArgumentException, TestFailedException {
        if (clazz == null) {
            throw new IllegalArgumentException("clazz == null");
        }
        Constructor con = assertOneConstructor(clazz);
        assertPrivateConstructor(con);
        assertNoExceptionFromConstructor(con);
    }

    private static Constructor assertOneConstructor(Class clazz) throws TestFailedException {
        Constructor[] cons = clazz.getDeclaredConstructors();
        int constructorCount = ArrayUtils.countElements(cons);
        if (constructorCount != 1) {
            throw new TestFailedException("Expected exactly 1 constructor in class " + clazz.getName() + ". However, " + constructorCount + " were found.");
        }
        return cons[0];
    }

    private static void assertPrivateConstructor(Constructor con) throws TestFailedException {
        int modifiers = con.getModifiers();
        if (Modifier.PRIVATE != modifiers) {
            String className = con.getDeclaringClass().getName();
            throw new TestFailedException("Expected " + className + " constructor to be private (modifiers==" + Modifier.PRIVATE + "). Instead: modifiers==" + modifiers + '.');
        }
    }

    private static void assertNoExceptionFromConstructor(Constructor con) throws TestFailedException {
        try {
            con.setAccessible(true);
            con.newInstance((Object[]) null);
        } catch (Throwable cause) {
            String className = con.getDeclaringClass().getName();
            throw new TestFailedException("Calling the " + className + " constructor resulted in an exception of class " + cause.getClass().getName() + ". The exception message is: " + TextUtils.quote(cause.getMessage()) + '.', cause);
        }
    }

    private TestUtils() {
    }
}