content: package org.example;
  
  import org.junit.jupiter.api.Test;
  import static org.junit.jupiter.api.Assertions.*;
  
  class AppTest {
  
      @Test
      void testCheckSign() {
          App app = new App();
          assertEquals("Positive", app.checkSign(10));
          assertEquals("Negative", app.checkSign(-1));
          assertEquals("Zero", app.checkSign(0));
      }
  
      @Test
      void testGetDayName() {
          App app = new App();
          assertEquals("Monday", app.getDayName(1));
          assertEquals("Sunday", app.getDayName(7));
          assertEquals("Invalid day", app.getDayName(9));
      }
  
      @Test
      void testCalculateFactorial() {
          App app = new App();
          assertEquals(120, app.calculateFactorial(5));
          assertEquals(1, app.calculateFactorial(0));
          assertEquals(720, app.calculateFactorial(6));
      }
  
      @Test
      void testIsPrime() {
          App app = new App();
          assertTrue(app.isPrime(7), "7 should be prime");
          assertFalse(app.isPrime(8), "8 should not be prime");
          assertFalse(app.isPrime(1), "1 is not prime by definition");
          assertFalse(app.isPrime(-5), "Negative numbers are not prime");
      }
  
      @Test
      void testSumUntil() {
          App app = new App();
          assertEquals(15, app.sumUntil(5), "1+2+3+4+5 = 15");
          assertEquals(1, app.sumUntil(1), "Limit=1 => 1");
          assertEquals(55, app.sumUntil(10), "1+2+...+10 = 55");
      }
  }
  