Add unit tests for configuration parsing and validation

[cbaugus]

Summary

The application reads numerous environment variables for configuration but has no tests for configuration parsing or validation logic. Invalid configurations can cause runtime panics or unexpected behavior.

Current Configuration Variables

Variable	Type	Required	Default
TARGET_URL	String	Yes	-
REQUEST_METHOD	String	No	"GET"
POST_BODY	JSON String	No	-
SKIP_TLS_VERIFY	bool	No	false
CLIENT_CERT_PATH	Path	No	-
CLIENT_KEY_PATH	Path	No	-
RESOLVE_TARGET_ADDR	IP:Port	No	-
CUSTOM_HEADERS	String	No	-
LOAD_MODEL	String	No	"concurrent"
MAX_CONCURRENT	u32	No	10
TARGET_RPS	f64	No	-
MIN_RPS	f64	No	-
MAX_RPS	f64	No	-
RAMP_DURATION	Duration	No	-
TEST_DURATION	Duration	No	"1m"
PEAK_RPS	f64	No	-
MIDDAY_RPS	f64	No	-
NIGHT_RPS	f64	No	-
Various phase durations	Duration	No	-

Test Cases Required

Required Variables

• Missing TARGET_URL produces clear error
• Empty TARGET_URL produces clear error
• Invalid URL format produces clear error

Load Model Selection

• LOAD_MODEL=concurrent selects Concurrent model
• LOAD_MODEL=rps selects Rps model (requires TARGET_RPS)
• LOAD_MODEL=ramp selects RampRps model (requires MIN_RPS, MAX_RPS, RAMP_DURATION)
• LOAD_MODEL=daily selects DailyTraffic model
• Unknown LOAD_MODEL value produces clear error
• Missing required params for model produces clear error

mTLS Configuration

• Both CLIENT_CERT_PATH and CLIENT_KEY_PATH required together
• Only cert without key produces error
• Only key without cert produces error
• Invalid cert path produces clear error
• Invalid key path produces clear error

Numeric Validation

• Negative MAX_CONCURRENT produces error
• Zero MAX_CONCURRENT produces error or warning
• Negative RPS values produce error
• MIN_RPS > MAX_RPS produces error

Duration Validation

• Invalid duration format produces clear error
• Zero duration produces warning or error
• Extremely long durations are accepted

DNS Override

• Valid RESOLVE_TARGET_ADDR format (IP:port) accepted
• Invalid format produces clear error
• IPv6 addresses handled correctly

Acceptance Criteria

• All environment variables have test coverage
• Missing required variables produce clear errors
• Invalid values produce descriptive error messages
• Default values are documented and tested
• mTLS requires both cert and key
• Load model parameters validated for each model type

Implementation Notes

This issue pairs well with #15 (Extract Config struct). Tests should:

1. Use temp_env or similar crate to set env vars in tests
2. Create a Config::from_env() function that can be unit tested
3. Return Result<Config, ConfigError> instead of panicking

Example Test Structure

#[cfg(test)]
mod config_tests {
    use super::*;
    use temp_env::with_vars;

    #[test]
    fn test_missing_target_url_error() {
        with_vars(vec![("TARGET_URL", None::<&str>)], || {
            let result = Config::from_env();
            assert!(result.is_err());
            assert!(result.unwrap_err().to_string().contains("TARGET_URL"));
        });
    }

    #[test]
    fn test_rps_model_requires_target_rps() {
        with_vars(vec![
            ("TARGET_URL", Some("https://example.com")),
            ("LOAD_MODEL", Some("rps")),
            // TARGET_RPS intentionally missing
        ], || {
            let result = Config::from_env();
            assert!(result.is_err());
        });
    }

    #[test]
    fn test_mtls_requires_both_cert_and_key() {
        with_vars(vec![
            ("TARGET_URL", Some("https://example.com")),
            ("CLIENT_CERT_PATH", Some("/path/to/cert.pem")),
            // CLIENT_KEY_PATH intentionally missing
        ], || {
            let result = Config::from_env();
            assert!(result.is_err());
        });
    }
}

Dependencies

• Consider using temp_env crate for testing environment variables
• This issue should be done after or alongside Refactor: Split main.rs into modular structure #15 (modular refactor)

Priority

Medium - Configuration errors currently cause panics with stack traces. Better validation would improve user experience.

[cbaugus]

Closed via PR #24. Added 16 unit tests for config parsing.

[cbaugus]

Closed via PR #24. Added 16 unit tests for config parsing.

[cbaugus]

Closed via PR #24.