Unit Test Boundary Conditions

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;
import static org.assertj.core.api.Assertions.*;

class IntegerBoundaryTest {

  @ParameterizedTest
  @ValueSource(ints = {Integer.MIN_VALUE, Integer.MIN_VALUE + 1, 0, Integer.MAX_VALUE - 1, Integer.MAX_VALUE})
  void shouldHandleIntegerBoundaries(int value) {
    assertThat(value).isNotNull();
  }

  @Test
  void shouldDetectIntegerOverflow() {
    assertThatThrownBy(() -> Math.addExact(Integer.MAX_VALUE, 1))
      .isInstanceOf(ArithmeticException.class);
  }

  @Test
  void shouldDetectIntegerUnderflow() {
    assertThatThrownBy(() -> Math.subtractExact(Integer.MIN_VALUE, 1))
      .isInstanceOf(ArithmeticException.class);
  }

  @Test
  void shouldHandleZeroEdge() {
    int result = MathUtils.divide(0, 5);
    assertThat(result).isZero();

    assertThatThrownBy(() -> MathUtils.divide(5, 0))
      .isInstanceOf(ArithmeticException.class);
  }
}

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;

class StringBoundaryTest {

  @ParameterizedTest
  @ValueSource(strings = {"", " ", "  ", "\t", "\n"})
  void shouldRejectEmptyAndWhitespace(String input) {
    boolean result = StringUtils.isNotBlank(input);
    assertThat(result).isFalse();
  }

  @Test
  void shouldHandleNullString() {
    String result = StringUtils.trim(null);
    assertThat(result).isNull();
  }

  @Test
  void shouldHandleSingleCharacter() {
    assertThat(StringUtils.capitalize("a")).isEqualTo("A");
    assertThat(StringUtils.trim("x")).isEqualTo("x");
  }

  @Test
  void shouldHandleVeryLongString() {
    String longString = "x".repeat(1000000);

    assertThat(longString.length()).isEqualTo(1000000);
    assertThat(StringUtils.isNotBlank(longString)).isTrue();
  }
}

class CollectionBoundaryTest {

  @Test
  void shouldHandleEmptyList() {
    List<String> empty = List.of();

    assertThat(empty).isEmpty();
    assertThat(CollectionUtils.first(empty)).isNull();
    assertThat(CollectionUtils.count(empty)).isZero();
  }

  @Test
  void shouldHandleSingleElementList() {
    List<String> single = List.of("only");

    assertThat(single).hasSize(1);
    assertThat(CollectionUtils.first(single)).isEqualTo("only");
    assertThat(CollectionUtils.last(single)).isEqualTo("only");
  }

  @Test
  void shouldHandleLargeList() {
    List<Integer> large = new ArrayList<>();
    for (int i = 0; i < 100000; i++) {
      large.add(i);
    }

    assertThat(large).hasSize(100000);
    assertThat(CollectionUtils.first(large)).isZero();
    assertThat(CollectionUtils.last(large)).isEqualTo(99999);
  }

  @Test
  void shouldHandleNullInCollection() {
    List<String> withNull = new ArrayList<>(List.of("a", null, "c"));

    assertThat(withNull).contains(null);
    assertThat(CollectionUtils.filterNonNull(withNull)).hasSize(2);
  }
}

class FloatingPointBoundaryTest {

  @Test
  void shouldHandleFloatingPointPrecision() {
    double result = 0.1 + 0.2;
    assertThat(result).isCloseTo(0.3, within(0.0001));
  }

  @Test
  void shouldHandleSpecialFloatingPointValues() {
    assertThat(Double.POSITIVE_INFINITY).isGreaterThan(Double.MAX_VALUE);
    assertThat(Double.NEGATIVE_INFINITY).isLessThan(Double.MIN_VALUE);
    assertThat(Double.NaN).isNotEqualTo(Double.NaN);
  }

  @Test
  void shouldHandleZeroInDivision() {
    assertThat(1.0 / 0.0).isEqualTo(Double.POSITIVE_INFINITY);
    assertThat(-1.0 / 0.0).isEqualTo(Double.NEGATIVE_INFINITY);
    assertThat(0.0 / 0.0).isNaN();
  }
}

class DateTimeBoundaryTest {

  @Test
  void shouldHandleMinAndMaxDates() {
    LocalDate min = LocalDate.MIN;
    LocalDate max = LocalDate.MAX;

    assertThat(min).isBefore(max);
    assertThat(DateUtils.isValid(min)).isTrue();
    assertThat(DateUtils.isValid(max)).isTrue();
  }

  @Test
  void shouldHandleLeapYearBoundary() {
    LocalDate leapYearEnd = LocalDate.of(2024, 2, 29);
    assertThat(leapYearEnd).isNotNull();
  }

  @Test
  void shouldRejectInvalidDateInNonLeapYear() {
    assertThatThrownBy(() -> LocalDate.of(2023, 2, 29))
      .isInstanceOf(DateTimeException.class);
  }
}

class ArrayBoundaryTest {

  @Test
  void shouldHandleFirstElementAccess() {
    int[] array = {1, 2, 3, 4, 5};
    assertThat(array[0]).isEqualTo(1);
  }

  @Test
  void shouldHandleLastElementAccess() {
    int[] array = {1, 2, 3, 4, 5};
    assertThat(array[array.length - 1]).isEqualTo(5);
  }

  @Test
  void shouldThrowOnNegativeIndex() {
    int[] array = {1, 2, 3};
    assertThatThrownBy(() -> array[-1])
      .isInstanceOf(ArrayIndexOutOfBoundsException.class);
  }

  @Test
  void shouldThrowOnOutOfBoundsIndex() {
    int[] array = {1, 2, 3};
    assertThatThrownBy(() -> array[10])
      .isInstanceOf(ArrayIndexOutOfBoundsException.class);
  }

  @Test
  void shouldHandleEmptyArray() {
    int[] empty = {};
    assertThat(empty.length).isZero();
    assertThatThrownBy(() -> empty[0])
      .isInstanceOf(ArrayIndexOutOfBoundsException.class);
  }
}