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.
npx agentmods add skills/skydoves/android-testing-skills/picking-test-doublesnpx skills add skydoves/android-testing-skills --skill picking-test-doublesgit clone --depth 1 https://github.com/skydoves/android-testing-skillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/skydoves/android-testing-skills/picking-test-doubles)<a href="https://agentmods.dev/skills/skydoves/android-testing-skills/picking-test-doubles"><img src="https://agentmods.dev/badge/skills/skydoves/android-testing-skills/picking-test-doubles.svg" alt="Measured on agentmods" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00193 | $0.04966 |
| Opus 5 | $0.00097 | $0.02483 |
| Sonnet 5 | $0.00039 | $0.00993 |
| Haiku 4.5 | $0.00019 | $0.00497 |
Grade A, and why
picking-test-doubles 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 5d 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.
How it starts
The opening of the file, as written. The whole thing — 415 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Picking Test Doubles — Prefer Fakes; Mocks for Interactions Only
Google has an unambiguous preference order for test doubles, stated three times on /training/testing/fundamentals/test-doubles. Most Android codebases over-mock and under-fake, which produces tests that pin implementation details (which methods were called) instead of behavior (what state the system landed in). This skill encodes the six doubles, the preference order verbatim, and a decision matrix for picking the right one. Framework-mechanics for the mocking libraries themselves live in sibling skills (../../../jvm-tests/mocking/mocking-with-mockito/SKILL.md, ../../../jvm-tests/mocking/mocking-with-mockk/SKILL.md).
When to use this skill
- The user asks "should I use a fake or a mock" / "Mockito or MockK" / "what's the difference between a stub and a spy".
- The user is replacing a dependency in a test and is unsure which double to reach for.
- The PR under review uses
verify(repo).getUser(any())everywhere and the agent suspects over-mocking. - The user mentions
Robolectric"shadows" and asks where they fit in the test-double taxonomy. - The user says "every { repo.getUser() } returns User('Alice')" with no behavior under test and the agent should suggest a fake.
When NOT to use this skill
- The user already picked a fake / mock and wants framework mechanics (
whenever/every/verify/argumentCaptor) — use../../../jvm-tests/mocking/mocking-with-mockito/SKILL.mdor../../../jvm-tests/mocking/mocking-with-mockk/SKILL.md. - The user is wiring Hilt to swap a binding — combine this skill with
../../strategies/applying-testing-strategies/SKILL.md(Hilt section). - The user is choosing what to test, not how — use
../../concepts/choosing-what-to-test/SKILL.md. - The user is debugging a Robolectric shadow that throws on a specific API — use
../../../jvm-tests/robolectric/using-robolectric-correctly/SKILL.md.
Prerequisites
- A test target whose dependencies are injected (constructor injection or interface-based DI). Doubles cannot be substituted into hard-wired singletons without refactor.
mockito-core+mockito-kotlinorio.mockk:mockkontestImplementationif mocks/stubs/spies are needed. See../../strategies/organizing-test-source-sets/SKILL.md.- For shadows:
org.robolectric:robolectricontestImplementationplustestOptions.unitTests.includeAndroidResources = true.
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.
- 5d ago First seen · 415 lines · 193 tokens per session scan A 537b057ed4ff
picking-test-doubles is a skill published in the GitHub repository skydoves/android-testing-skills (317 stars, last pushed 3mo ago), licensed Apache-2.0. It adds 193 tokens to every session and 4,966 once invoked, about $0.0010 per session on Opus 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 2026-08-30.
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