content: import static org.junit.jupiter.api.Assertions.assertEquals;
  
  import org.junit.jupiter.api.BeforeEach;
  import org.junit.jupiter.api.Test;
  
  public class SubstringTest {
      private Substring substring;
  
      @BeforeEach
      void setup() {
          substring = new Substring();
      }
  
      @Test
      void sample() {
          // start는 포함, end는 포함하지 않음.
          assertEquals("lowo", substring.substring("Helloworld", 3, 7));
      }
  
      @Test
      void simple() {
          assertEquals("", substring.substring("Hello", 0, 0));
          assertEquals("H", substring.substring("Hello", 0, 1));
          assertEquals("He", substring.substring("Hello", 0, 2));
      }
  
      @Test
      void range() {
          assertEquals("", substring.substring("Hello", 1, 1));
          assertEquals("e", substring.substring("Hello", 1, 2));
          assertEquals("el", substring.substring("Hello", 1, 3));
      }
  
      @Test
      void error() {
          assertEquals("", substring.substring("Hello", 1, 0));
          assertEquals("", substring.substring("12345", 5, 10));
          assertEquals("45", substring.substring("12345", 3, 10));
          assertEquals("12", substring.substring("12345", -10, 2));
      }
  }
  