[PATCH v1 18/28] rust: str: add `CStr` unit tests

[Miguel Ojeda <ojeda@kernel.org>]

From: Milan Landaverde <milan@mdaverde.com>

Add unit tests for `CStr::from_bytes_with_nul()` and
`CStr::from_bytes_with_nul_unchecked()`.

These serve as an example of the first unit tests for Rust code
(i.e. different from documentation tests).

Signed-off-by: Milan Landaverde <milan@mdaverde.com>
[Reworded, adapted for upstream and applied latest changes]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 rust/kernel/str.rs | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 11d297c1a61c..3ed685cb5a3c 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -321,6 +321,35 @@ where
     }
 }
 
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_cstr_to_str() {
+        let good_bytes = b"\xf0\x9f\xa6\x80\0";
+        let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
+        let checked_str = checked_cstr.to_str().unwrap();
+        assert_eq!(checked_str, "🦀");
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_cstr_to_str_panic() {
+        let bad_bytes = b"\xc3\x28\0";
+        let checked_cstr = CStr::from_bytes_with_nul(bad_bytes).unwrap();
+        checked_cstr.to_str().unwrap();
+    }
+
+    #[test]
+    fn test_cstr_as_str_unchecked() {
+        let good_bytes = b"\xf0\x9f\x90\xA7\0";
+        let checked_cstr = CStr::from_bytes_with_nul(good_bytes).unwrap();
+        let unchecked_str = unsafe { checked_cstr.as_str_unchecked() };
+        assert_eq!(unchecked_str, "🐧");
+    }
+}
+
 /// Allows formatting of [`fmt::Arguments`] into a raw buffer.
 ///
 /// It does not fail if callers write past the end of the buffer so that they can calculate the
-- 
2.38.1