Agent skill · dotnet
testability-obstacle
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.
What it needs
About 9k tokens when loaded.
What this skill does
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-agent. 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 TimeProvider or IFileSystem and asks to migrate call sites to it. Use migrate-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. If an adequate seam already exists, stop refactoring and use it. This skill adds no value when a fake can already be supplied. …
How to use it
Reference it in AdaL, Claude Code, Cursor or any coding agent — nothing to install:
@skills dotnet/testability-obstacle