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new 9ed3d554 warn about culture sensitive substring assertions
9ed3d554 is described below
commit 9ed3d554ffdbd08fc64cb06fbfa20b012b23a170
Author: Jan Friedrich <[email protected]>
AuthorDate: Wed Sep 2 06:30:40 2026 +0200
warn about culture sensitive substring assertions
Does.Contain has no comparison parameter, and linguistic comparison skips
ignorable characters, so Does.Not.Contain matches a NUL that is not there.
It
cost a red CI on two escape tests.
---
CLAUDE.md | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/CLAUDE.md b/CLAUDE.md
index ecbe7c6a..548b9144 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -153,6 +153,12 @@ almost always be doing.
- Drive a test over a background thread with gates (`ManualResetEventSlim`),
never with
`Thread.Sleep`: park the worker, assert the state you care about, then
release it. See
`BackgroundSenderTest`, where every wait has a generous timeout and the
assertions are exact.
+- **`Does.Contain` is culture sensitive and cannot be made ordinal**: its
`ContainsConstraint` has
+ no comparison parameter. Linguistic comparison skips ignorable characters,
so `Does.Not.Contain`
+ reports a match for NUL, soft hyphen or a zero-width character in a string
that holds none. When
+ the assertion is about control characters, use
+ `Contains.Substring(x).Using(StringComparison.Ordinal)`, negated with the
`!` operator that
+ `Constraint` defines, or assert the whole value with `Is.EqualTo`, which is
ordinal.
- Mark a test `[NonParallelizable]` when it mutates static state
(`LogLog.InternalDebugging`, a
static field on a test double, a process-wide native registration).
- Wrap expected internal logging in
`LogLog.ExecuteWithoutEmittingInternalMessages(...)` and capture
