jdk/test/jdk/java/util/Comparator/MinMaxTest.java

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/**
 * @test
 * @bug 8356995
 * @summary Comparator min/max method tests
 * @run junit MinMaxTest
 */

import org.junit.jupiter.api.Test;

import java.util.Comparator;

import static org.junit.jupiter.api.Assertions.*;

public class MinMaxTest {
  @Test
  void testMin() {
    Comparator<String> c = Comparator.naturalOrder();
    assertEquals("a", c.min("a", "b"));
    assertEquals("a", c.min("b", "a"));
  }

  @Test
  void testMax() {
    Comparator<String> c = Comparator.naturalOrder();
    assertEquals("b", c.max("a", "b"));
    assertEquals("b", c.max("b", "a"));
  }

  @Test
  void testThrowsNPE() {
    Comparator<String> c = Comparator.naturalOrder();
    assertThrows(NullPointerException.class, () -> c.min(null, "a"));
    assertThrows(NullPointerException.class, () -> c.min("a", null));
    assertThrows(NullPointerException.class, () -> c.max(null, "a"));
    assertThrows(NullPointerException.class, () -> c.max("a", null));
  }

  @Test
  void testThrowsCCE() {
    @SuppressWarnings("unchecked")
    Comparator<Object> c = (Comparator<Object>) (Comparator<?>)Comparator.naturalOrder();
    assertThrows(ClassCastException.class, () -> c.min(1, "a"));
    assertThrows(ClassCastException.class, () -> c.min("a", 1));
    assertThrows(ClassCastException.class, () -> c.max(1, "a"));
    assertThrows(ClassCastException.class, () -> c.max("a", 1));
  }

  @Test
  void testEqualReturnFirst() {
    Comparator<Object> allEqual = (_, _) -> 0;
    Object o1 = new Object();
    Object o2 = new Object();
    assertSame(o1, allEqual.min(o1, o2));
    assertSame(o1, allEqual.max(o1, o2));
  }

  @Test
  void testComparatorSubtype() {
    Comparator<CharSequence> byLength = Comparator.comparing(CharSequence::length);
    String s1 = "long_string";
    String s2 = "short";
    String min = byLength.min(s1, s2);
    String max = byLength.max(s1, s2);
    assertEquals(s1, max);
    assertEquals(s2, min);
  }
}