20180111_kata_lunch : https://www.hackerrank.com/challenges/staircase/problem

StairCaseSolution.java

import java.util.Arrays;

public class StairCaseSolution {
    public static String staircase(int n) {
        if (n <= 0)
            return "";
        StringBuilder resultBuilder = new StringBuilder();
        for (int spaceNumber = n - 1; spaceNumber >= 0; spaceNumber--) {
            resultBuilder.append(createLine(n, spaceNumber)).append('\n');
        }
        resultBuilder.deleteCharAt(resultBuilder.length()-1);
        return resultBuilder.toString();
    }

    private static char[] createLine(int sharpNumber, int spaceNumber) {
        char[] line = new char[sharpNumber];
        Arrays.fill(line, 0, spaceNumber, ' ');
        Arrays.fill(line,spaceNumber, sharpNumber, '#');
        return line;
    }
}

StairCaseTest.java

import org.junit.Test;

import static org.junit.Assert.assertEquals;

public class StairCaseTest {
    @Test
    public void should_return_empty_string_when_given_0(){
        assertEquals("", StairCaseSolution.staircase(0));
    }

    @Test
    public void should_return_empty_string_when_given_minus10(){
        assertEquals("", StairCaseSolution.staircase(-10));
    }

    @Test
    public void should_return_sharp_when_given_1(){
        assertEquals("#", StairCaseSolution.staircase(1));
    }

    @Test
    public void should_return_01n11__when_given_2(){
        assertEquals(" #\n##", StairCaseSolution.staircase(2));
    }
    @Test
    public void should_return_001n011n111__when_given_3(){
        assertEquals("  #\n ##\n###", StairCaseSolution.staircase(3));
    }
}