test: fix vacuous assertions in create_work_item and update_work_item (#1603)

Replace bare assert!(result.is_err()) with unwrap_err() + message content
checks so each test verifies the specific validation rule that was violated,
not just that some error was returned.

Also add descriptive messages to the bare ensure!() calls in
CreateWorkItemParams::validate() so the tests have something meaningful to
assert against.

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

src/safe_outputs/create_work_item.rs

@@ -30,8 +30,11 @@ pub struct CreateWorkItemParams {
 
 impl Validate for CreateWorkItemParams {
     fn validate(&self) -> anyhow::Result<()> {
-        ensure!(self.title.len() > 5);
-        ensure!(self.description.len() > 30);
+        ensure!(self.title.len() > 5, "title must be more than 5 characters");
+        ensure!(
+            self.description.len() > 30,
+            "description must be more than 30 characters"
+        );
         for tag in &self.tags {
             ensure!(
                 !tag.contains(';'),
@@ -561,7 +564,11 @@ mod tests {
             tags: vec![],
         };
         let result: Result<CreateWorkItemResult, _> = params.try_into();
-        assert!(result.is_err());
+        let err = result.unwrap_err().to_string();
+        assert!(
+            err.contains("title must be more than 5 characters"),
+            "Expected title length error, got: {err}"
+        );
     }
 
     #[test]
@@ -572,7 +579,11 @@ mod tests {
             tags: vec![],
         };
         let result: Result<CreateWorkItemResult, _> = params.try_into();
-        assert!(result.is_err());
+        let err = result.unwrap_err().to_string();
+        assert!(
+            err.contains("description must be more than 30 characters"),
+            "Expected description length error, got: {err}"
+        );
     }
 
     #[test]
@@ -583,7 +594,11 @@ mod tests {
             tags: vec!["tag-one; tag-two".to_string()],
         };
         let result: Result<CreateWorkItemResult, _> = params.try_into();
-        assert!(result.is_err());
+        let err = result.unwrap_err().to_string();
+        assert!(
+            err.contains("semicolon"),
+            "Expected semicolon error, got: {err}"
+        );
     }
 
     #[test]

src/safe_outputs/update_work_item.rs

@@ -643,7 +643,11 @@ mod tests {
             tags: None,
         };
         let result: Result<UpdateWorkItemResult, _> = params.try_into();
-        assert!(result.is_err());
+        let err = result.unwrap_err().to_string();
+        assert!(
+            err.contains("255 characters or fewer"),
+            "Expected title length error, got: {err}"
+        );
     }
 
     #[test]