test(config): add comprehensive validation tests for malformed configuration

pkg/apperrors/apperrors.go

@@ -7,6 +7,8 @@ import "errors"
 var (
 	ErrTemplateEmpty               = errors.New("template cannot be empty")
 	ErrTimestampFormatEmpty        = errors.New("timestamp format cannot be empty")
+	ErrInvalidTimestampFormat      = errors.New("invalid timestamp format")
+	ErrInvalidTimezone             = errors.New("invalid timezone")
 	ErrInvalidColor                = errors.New("invalid color")
 	ErrInvalidUserFormat           = errors.New("invalid user format")
 	ErrInvalidPIDFormat            = errors.New("invalid PID format")
@@ -16,6 +18,8 @@ var (
 	ErrInvalidStderrLogLevel       = errors.New("invalid default stderr log level")
 	ErrInvalidLogLevel             = errors.New("invalid log level")
 	ErrNoDetectionKeywords         = errors.New("log level has no detection keywords")
+	ErrEmptyKeyword                = errors.New("empty keyword in detection keywords")
+	ErrDetectionDisabledWithKeywords = errors.New("detection disabled but keywords are configured")
 )
 
 // Command line errors.

pkg/config/validation.go

@@ -153,6 +153,11 @@ func (c *Config) validateLogLevel() error {
 			apperrors.ErrInvalidStderrLogLevel, c.LogLevel.DefaultStderr, strings.Join(validLevels, ", "))
 	}
 
+	// Check for conflicting configuration: detection disabled but keywords provided
+	if !c.LogLevel.Detection.Enabled && len(c.LogLevel.Detection.Keywords) > 0 {
+		return apperrors.ErrDetectionDisabledWithKeywords
+	}
+
 	for level, keywords := range c.LogLevel.Detection.Keywords {
 		if !isValidLogLevel(strings.ToUpper(level), validLevels) {
 			return fmt.Errorf("%w '%s' in detection keywords", apperrors.ErrInvalidLogLevel, level)
@@ -161,6 +166,14 @@ func (c *Config) validateLogLevel() error {
 		if len(keywords) == 0 {
 			return fmt.Errorf("%w '%s'", apperrors.ErrNoDetectionKeywords, level)
 		}
+
+		// Check for empty strings in keywords
+		//nolint:modernize // Need to return error with level context, not just check existence
+		for _, keyword := range keywords {
+			if keyword == "" {
+				return fmt.Errorf("%w for level '%s'", apperrors.ErrEmptyKeyword, level)
+			}
+		}
 	}
 
 	return nil