131-java-testing-unit-testing

131-java-testing-unit-testing is a skill for Claude Code, Codex from jabrena/cursor-rules-examples. It costs 113 tokens per session (609 once invoked), scanned A, original, Apache-2.0.

Guidance for writing Java unit tests with JUnit 5, AssertJ, and Mockito. Unit tests check small parts of a program in isolation, while mocks stand in for their dependencies.

In plain words
What is it for?
Use it to write or review Java tests, migrate from JUnit 4 to JUnit 5, structure tests with Given-When-Then, mock dependencies, add parameterized cases, and assess coverage.
Why use it?
It helps replace fragile or unclear tests with independent tests that explain expected behavior and cover errors, varied inputs, and boundary cases.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: installed under .agents/ (shared by several agents).

Good fit Use it to write or review Java tests, migrate from JUnit 4 to JUnit 5, structure tests with Given-When-Then, mock dependencies, add parameterized cases, and assess coverage.

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Install with agentmods
npx agentmods add skills/jabrena/cursor-rules-examples/131-java-testing-unit-testing
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add jabrena/cursor-rules-examples --skill 131-java-testing-unit-testing
Clone the repo
git clone --depth 1 https://github.com/jabrena/cursor-rules-examples

Made for: Claude Code, Codex.

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README.md
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Per session 113 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 609 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00113 $0.00609
Opus 5.5 $0.00045 $0.00244
Sonnet 5.5 $0.00023 $0.00122
Haiku 4.5 $0.00011 $0.00061

Measured 1mo ago against content hash ad214c3a59c4, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

131-java-testing-unit-testing scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.agents/skills/131-java-testing-unit-testing/SKILL.md · 46 lines

What it actually says

Java Unit testing guidelines

Review and improve Java unit tests using modern JUnit 5, AssertJ, and Mockito best practices.

What is covered in this Skill?

  • JUnit 5 annotations: @Test, @BeforeEach, @AfterEach, @DisplayName, @Nested, @ParameterizedTest
  • AssertJ fluent assertions: assertThat, assertThatThrownBy
  • Given-When-Then test structure, descriptive test naming, single-responsibility tests
  • Test independence and isolated state
  • Parameterized tests: @ValueSource/@CsvSource/@MethodSource
  • Mockito dependency mocking: @Mock, @InjectMocks, MockitoExtension
  • Code coverage guidance (JaCoCo), package-private test visibility
  • Testing anti-patterns: reflection, shared state, hard-coded values, testing implementation details
  • Error handling: assertThatThrownBy, exception messages
  • JSpecify null-safety: @NullMarked, @Nullable
  • RIGHT-BICEP coverage principles, A-TRIP test quality, CORRECT boundary condition verification

Scope: The reference is organized by examples (good/bad code patterns) for each core area. Apply recommendations based on applicable examples.

Constraints

Before applying any unit test changes, ensure the project compiles. If compilation fails, stop immediately — do not proceed until resolved. After applying improvements, run full verification.

  • MANDATORY: Run ./mvnw compile or mvn compile before applying any change
  • SAFETY: If compilation fails, stop immediately and do not proceed — compilation failure is a blocking condition
  • VERIFY: Run ./mvnw clean verify or mvn clean verify after applying improvements
  • BEFORE APPLYING: Read the reference for detailed examples, good/bad patterns, and constraints

When to use this skill

  • Review Java code for unit tests
  • Apply best practices for unit tests in Java code

Reference

For detailed guidance, examples, and constraints, see references/131-java-testing-unit-testing.md.

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 1mo ago First seen · 46 lines · 113 tokens per session scan A ad214c3a59c4

Subscribe to this mod's changes

131-java-testing-unit-testing is a skill published in the GitHub repository jabrena/cursor-rules-examples (2 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 113 tokens to every session and 609 once invoked, about $0.0005 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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