Copilot instructions

1# Test file review rules
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3Applies to: tests/**/*.cs
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5These rules apply when reviewing test files in this repository.
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7## Test framework patterns — do NOT flag
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9- `[RunOn]` inherits from `TestMethodAttribute` (see `tests/Microsoft.Identity.Test.Integration.netcore/Infrastructure/TargetFramework.cs` line 15). Tests decorated with `[RunOn]` WILL be discovered by MSTest. Do not flag as missing `[TestMethod]`.
10- `Assert.IsTrue(bool?)` is a valid MSTest overload. Do not flag nullable bool arguments as type mismatches.
11- `Assert.DoesNotContain(substring, value)` — in MSTest v4, the first argument is the substring and the second is the value to search. Do not suggest swapping arguments.
12- `Assert.HasCount(expected, collection)` — valid MSTest v4 assertion. Do not suggest `Assert.AreEqual` for count checks.
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14## Test conventions
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16- Use MSTest SDK v4 with NSubstitute for mocking
17- Use `// Arrange`, `// Act`, `// Assert` comments
18- Prefer deterministic tests: avoid `Thread.Sleep`, timing dependencies, or environment-specific behavior
19- Copy existing style in nearby files for test method names
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21## Scope
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23- Only comment on test code that is added or modified in the PR diff
24- Do not comment on pre-existing test patterns or style
25- Do not re-post comments already made on earlier commits
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