feat(cli): add exit code tests and SerializationError variant

Add exit code verification tests (code 2 for clap errors, code 1 for
runtime errors). Add SerializationError variant to StringyError and
migrate JSON serialization errors from ConfigError to the new variant
for more precise error categorization.

Signed-off-by: UncleSp1d3r <unclesp1d3r@evilbitlabs.io>

Author: unclesp1d3r

src/output/json.rs

@@ -11,12 +11,12 @@ pub fn format_json(strings: &[FoundString], _metadata: &OutputMetadata) -> Resul
     let mut lines = Vec::with_capacity(strings.len());
     for item in strings {
         if !item.confidence.is_finite() {
-            return Err(StringyError::ConfigError(
+            return Err(StringyError::SerializationError(
                 "JSON serialization failed: non-finite confidence".to_string(),
             ));
         }
         let line = serde_json::to_string(item).map_err(|err| {
-            StringyError::ConfigError(format!("JSON serialization failed: {}", err))
+            StringyError::SerializationError(format!("JSON serialization failed: {}", err))
         })?;
         lines.push(line);
     }
@@ -275,8 +275,8 @@ mod tests {
         let strings = vec![make_string("nan").with_confidence(f32::NAN)];
         let result = format_json(&strings, &make_metadata(1));
         match result {
-            Err(StringyError::ConfigError(_)) => {}
-            _ => panic!("Expected ConfigError on invalid JSON serialization"),
+            Err(StringyError::SerializationError(_)) => {}
+            _ => panic!("Expected SerializationError on invalid JSON serialization"),
         }
     }
 }

src/types/error.rs

@@ -18,6 +18,9 @@ pub enum StringyError {
     #[error("Configuration error: {0}")]
     ConfigError(String),
 
+    #[error("Serialization error: {0}")]
+    SerializationError(String),
+
     #[error("Validation error: {0}")]
     ValidationError(String),
 

tests/integration_cli_errors.rs

@@ -25,3 +25,15 @@ fn error_missing_file_shows_path() {
         .failure()
         .stderr(predicate::str::contains("this_file_does_not_exist.bin"));
 }
+
+#[test]
+fn exit_code_2_for_clap_errors() {
+    // Missing required argument
+    stringy().assert().failure().code(2);
+}
+
+#[test]
+fn exit_code_1_for_runtime_errors() {
+    // Cargo.toml is not a valid binary format
+    stringy().arg("Cargo.toml").assert().failure().code(1);
+}