It's all wrong, the test cases for submit are wrong. Should be something like this.

import java.util.Random;
import static org.junit.Assert.assertEquals;
import org.junit.Test;

public class PruebasCelsius {
String solution(int temperture) {
int c = (int) ((temperture - 32) * (5/9.0));
return c + (c <= 0 ? " is freezing temperature" : " is above freezing temperature");
}

@Test
public void test1() {
    assertEquals(solution(56), GrassHopper.weatherInfo(56));
}
@Test
public void test2() {
    assertEquals(solution(23), GrassHopper.weatherInfo(23));
}
@Test
public void test3() {
    assertEquals(solution(33), GrassHopper.weatherInfo(33));
}
@Test
public void test4() {
    assertEquals(solution(5), GrassHopper.weatherInfo(5));
}
@Test
public void test5() {
    Random rand = new Random();
    for (int i = 0; i < 50; i++) {
        int num = rand.nextInt(100)+1;
        assertEquals(solution(num), GrassHopper.weatherInfo(num));
    }
}

}