import org.junit.runner.JUnitCore;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;

public class TestRunnerStringMethods {
	public static void main(String[] args) {
		Result result = JUnitCore.runClasses(TestJunitMyIndexOf.class);
		for (Failure failure : result.getFailures()) {
			System.out.println(failure.toString());
		}
		System.out.println(result.wasSuccessful());
	}
}


String nullString = null;

public static int myIndexOf(char[] str, int ch, int index) {
    if (str == null) {
        // output NullPointerException
    }
    if (str.length <= index || index < 0) {
        return -1;
    }
    for (int i = index; i < str.length; i++) {
        if (index == str[i]) {
            return i;
        }
    }
    // if not found
    return -1;
}

assertEquals(nullString.indexOf(3), StringMethods.myIndexOf(null, 'd',3));


OUTPUT:

testMyIndexOf2(TestingStringMethods.TestJunitMyIndexOf): null
false