Testability Obstacle
MUST USE for C#/.NET deterministic tests that require the smallest production seam for...
Install
npx skills add managedcode/dotnet-skills --skill testability-obstacle -g -a claude-code -y- Repository
- managedcode/dotnet-skills500
- Category
- Testing
- Updated
- 6d ago
- License
- MIT
- Context cost
- Mediumabout 3,000 tokens
- Runs scripts
- No, instructions only
What it does
MUST USE for C#/.NET deterministic tests that require the smallest production seam for DateTime/Task.Delay/File/Environment/Guid/Random, static API preservation, nested/parallel overrides, or no real I/O. USE ONLY when the target workspace contains C# source plus a .csproj or .sln. DO NOT USE for audits, bulk migration, code that already has an injectable seam, or an explicit migration to a user-named existing abstraction (migrate-static-to-wrapper). Use instead of general test generation when the requested test is impossible without a production edit and seam selection is still open.
Resolve a Testability Obstacle
Introduce the smallest behavior-preserving seam needed to test a specific C# behavior, then add deterministic tests that prove both the behavior and the seam. The production edit is a means to the requested test, not an invitation to redesign adjacent code.
When to Use
- A requested test would otherwise read/write the real filesystem.
- Behavior depends on the current time, delay, random value, environment, console, process, or another ambient dependency.
- The user explicitly permits or requests a safe production seam.
- Existing tests cannot control a dependency without process-global mutation.
When Not to Use
- The dependency is already injected or passed as an argument. Write tests with
a fake through the existing seam using
code-testing. - The user wants a repository-wide testability audit. Use
detect-static-dependencies. - The user wants wrappers generated but not call sites/tests changed. Use
generate-testability-wrappers. - The user requests a broad mechanical migration. Use
migrate-static-to-wrapper, then generate tests separately. - The user already selected an existing replacement such as
TimeProviderorIFileSystemand asks to migrate call sites to it. Usemigrate-static-to-wrapper, which also updates affected tests. - The code is not C#/.NET.
Inputs
| Input | Required | Description |
|---|---|---|
| Behavior to test | Yes | The method/workflow and expected observable behavior |
| Target scope | No | Discover the narrowest relevant file/project when omitted |
| Allowed production changes | No | Default to the minimum internal/constructor seam |
Workflow
Step 1: Prove the obstacle
Read the target production path and its existing tests. Identify the exact ambient operation preventing a deterministic test and the behavior that must remain unchanged. Do not run a repository-wide static scan for a single-class request.
