unit-test-boundary-conditions

Q: How do I install unit-test-boundary-conditions?

Run npx skills add https://github.com/giuseppe-trisciuoglio/developer-kit --skill unit-test-boundary-conditions in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/unit-test-boundary-conditions/ (personal) or .claude/skills/unit-test-boundary-conditions/ (project).

by giuseppe-trisciuoglioTesting & QA

Provides edge case, corner case, boundary condition, and limit testing patterns for Java unit tests. Validates minimum/maximum values, null cases, empty collections, numeric overflow/underflow, floating-point precision, and off-by-one scenarios using JUnit 5 and AssertJ. Use when writing .java test files to ensure code handles limits, corner cases, and special inputs correctly.

Installs: 4.1K
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Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/giuseppe-trisciuoglio/developer-kit --skill unit-test-boundary-conditions

01
Install
Run the command in your project. The CLI asks which agents to install for.
02
Describe the task
Ask your agent for something this skill covers. It loads unit-test-boundary-conditions automatically when relevant.
03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.

Security audits

Independent scans of the skill's instructions and bundled files.

Gen Agent Trust Hub PassSAFE ·This skill provides safe design pattern documentation and reference examples for writing Java unit tests addressing boundary conditions, edge cases, and arithmetic limits using JUnit 5 and AssertJ.

Socket PassNo alerts

Snyk PassLOW ·Risk: LOW · No issues

Runlayer WarnMEDIUM ·1/1 file flagged

ZeroLeaks PassNONE ·Score: 93/100 · 2 sections analyzed

SKILL.md

The instructions your agent reads when the skill is triggered.

Unit Testing Boundary Conditions and Edge Cases

Overview

Systematic patterns for testing boundary conditions, corner cases, and limit values in Java using JUnit 5. Covers numeric boundaries, string edge cases, collection states, floating-point precision, date/time limits, and off-by-one scenarios.

When to Use

Numeric min/max limits, null/empty/whitespace inputs
Overflow/underflow validation, collection boundaries
Off-by-one errors, floating-point precision

Instructions

Identify boundaries: List numeric limits (MIN_VALUE, MAX_VALUE, zero), string states (null, empty, whitespace), collection sizes (0, 1, many)
Apply parameterized tests: Use @ParameterizedTest with @ValueSource or @CsvSource for multiple boundary values
Test both sides of boundaries: Cover values just below, at, and just above each boundary
Run tests after adding each boundary category to catch issues early
Verify floating-point precision: Use isCloseTo(expected, within(tolerance)) with AssertJ
Test collection states: Explicitly test empty (0), single (1), and many (>1) element scenarios
Handle overflow/underflow: Use Math.addExact() and Math.subtractExact() to detect arithmetic overflow
Test date/time edges: Verify leap years, month boundaries, timezone transitions
Iterate based on failures: When a boundary test fails, analyze the error to discover additional untested boundaries; add test cases for the newly discovered edge conditions

Examples

Requires: junit-jupiter, junit-jupiter-params, assertj-core.

Integer Boundary Testing

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);
  }
}

String Boundary Testing

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();
  }
}

Collection Boundary Testing

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);
  }
}

Floating-Point Boundary Testing

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();
  }
}

Date/Time Boundary Testing

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);
  }
}

Array Index Boundary Testing

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);
  }
}

Best Practices

Test at boundaries explicitly: don't rely on random testing
Test null and empty separately from valid inputs
Use parameterized tests for multiple boundary cases
Test both sides of boundaries (just below, at, just above)
Verify error messages for invalid boundary inputs
Document why specific boundaries matter for your domain
Test overflow/underflow for all numeric operations

Constraints and Warnings

Integer overflow: Use Math.addExact() to detect silent overflow
Floating-point precision: Never use exact equality; always use tolerance-based assertions
NaN behavior: NaN != NaN; use Float.isNaN() or Double.isNaN()
Collection size limits: Be mindful of memory with large test collections
String encoding: Test with Unicode characters for internationalization
Date/time boundaries: Account for timezone transitions and daylight saving
Array indexing: Always test index 0, length-1, and out-of-bounds

References

Integer.MIN_VALUE/MAX_VALUE
Double.MIN_VALUE/MAX_VALUE
AssertJ Floating Point
Boundary Value Analysis
references/concurrent-testing.md - Thread safety patterns
references/parameterized-patterns.md - Off-by-one and parameterized examples

FAQ

What does the unit-test-boundary-conditions skill do?

How do I install unit-test-boundary-conditions?

Run npx skills add https://github.com/giuseppe-trisciuoglio/developer-kit --skill unit-test-boundary-conditions in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/unit-test-boundary-conditions/ (personal) or .claude/skills/unit-test-boundary-conditions/ (project).

Which AI agents can use unit-test-boundary-conditions?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is unit-test-boundary-conditions safe to install?

Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed; Runlayer flagged items to review; ZeroLeaks passed. As with any skill, read the SKILL.md and bundled scripts before installing.

Who maintains unit-test-boundary-conditions?

It is published by giuseppe-trisciuoglio in giuseppe-trisciuoglio/developer-kit. It has 4,075 recorded installs.