improve error messages with context (#13)

Signed-off-by: Jason Hall <jason@chainguard.dev>

tests/error_messages.rs

@@ -0,0 +1,61 @@
+//! Tests for enhanced error messages
+
+use std::fs;
+use tempfile::TempDir;
+use testscript_rs::run_test;
+
+#[test]
+fn test_error_messages() {
+    let temp_dir = TempDir::new().unwrap();
+    let script_path = temp_dir.path().join("failing_test.txt");
+
+    let script_content = r#"# Test that should fail with good error message
+exec echo "this works"
+stdout "this works"
+
+# This command will fail
+exec nonexistent-command arg1 arg2
+stdout "should not get here"
+
+# More context
+exec echo "after failure""#;
+
+    fs::write(&script_path, script_content).unwrap();
+
+    let result = run_test(&script_path);
+
+    // This should fail, but with enhanced error messages
+    assert!(result.is_err());
+
+    let error_msg = result.unwrap_err().to_string();
+    println!("Enhanced error message:\n{}", error_msg);
+
+    // Verify the error contains context
+    assert!(error_msg.contains("failing_test.txt"));
+    assert!(error_msg.contains("line"));
+    assert!(error_msg.contains("nonexistent-command"));
+}
+
+#[test]
+fn test_parse_error_context() {
+    let temp_dir = TempDir::new().unwrap();
+    let script_path = temp_dir.path().join("parse_error.txt");
+
+    let script_content = r#"# Test parse error
+exec echo "good command"
+[unclosed condition exec echo "bad"
+exec echo "after error""#;
+
+    fs::write(&script_path, script_content).unwrap();
+
+    let result = run_test(&script_path);
+
+    assert!(result.is_err());
+
+    let error_msg = result.unwrap_err().to_string();
+    println!("Parse error message:\n{}", error_msg);
+
+    // Should show context around the parse error
+    assert!(error_msg.contains("parse_error.txt"));
+    assert!(error_msg.contains("unclosed"));
+}