foxhunt/ml/tests/q_value_constraint_test.rs

//! Q-value Constraint Tests - Wave 14 Agent 27
//!
//! Tests for the Q-value collapse detection constraint.
//!
//! Bug Fix: Previous implementation incorrectly rejected negative Q-values
//! using `avg_q < 0.01`, which flagged valid negative Q-values as collapsed.
//!
//! Trading Context: Negative Q-values are VALID because they represent:
//! - Transaction costs
//! - Penalties (hold penalty, flip-flop penalty)
//! - Trading fees
//! - Negative expected returns in poor market conditions
//!
//! True Collapse: Q-values near zero (|q| < 0.01), not negative Q-values.

#[cfg(test)]
mod q_value_constraint_tests {
    /// Helper function to check if Q-value is collapsed
    /// This mirrors the logic that should be in dqn.rs
    fn is_q_value_collapsed(avg_q_value: f32) -> bool {
        // Check ABSOLUTE VALUE to detect true collapses near zero
        // Negative Q-values are valid in trading
        avg_q_value.abs() < 0.01
    }

    #[test]
    fn test_negative_q_values_valid() {
        // GIVEN: Trading DQN with negative Q-values (costs dominate rewards)
        // These are real values from Wave 13 that were incorrectly rejected
        let test_cases = vec![
            -3.37,  // Valid negative Q-value (high costs)
            -43.32, // Valid large negative Q-value
            -2.1,   // Valid moderate negative Q-value
            -0.5,   // Valid small negative Q-value (|q| = 0.5 > 0.01)
        ];

        for avg_q_value in test_cases {
            // WHEN: Constraint check is performed
            let is_collapsed = is_q_value_collapsed(avg_q_value);

            // THEN: Should NOT be flagged as collapsed
            assert!(
                !is_collapsed,
                "Negative Q-value {} should be VALID in trading (|q| = {:.4} > 0.01)",
                avg_q_value,
                avg_q_value.abs()
            );
        }
    }

    #[test]
    fn test_near_zero_q_values_invalid() {
        // GIVEN: Q-values near zero (true collapse)
        // These indicate the network is not learning meaningful value estimates
        let test_cases = vec![
            0.009,   // Positive near-zero
            -0.009,  // Negative near-zero
            0.0,     // Exact zero
            0.005,   // Small positive
            -0.005,  // Small negative
            0.0099,  // Just below threshold
            -0.0099, // Just below threshold (negative)
        ];

        for avg_q_value in test_cases {
            // WHEN: Constraint check is performed
            let is_collapsed = is_q_value_collapsed(avg_q_value);

            // THEN: Should be flagged as collapsed
            assert!(
                is_collapsed,
                "Q-value {} (|q| = {:.4} < 0.01) should be flagged as collapsed",
                avg_q_value,
                avg_q_value.abs()
            );
        }
    }

    #[test]
    fn test_large_magnitude_q_values_valid() {
        // GIVEN: Q-values with large magnitude (either sign)
        // These indicate the network is learning meaningful value estimates
        let test_cases = vec![
            10.5,   // Large positive
            -43.32, // Large negative (Wave 13 false positive)
            0.5,    // Medium positive
            -2.1,   // Medium negative
            0.01,   // Exactly at threshold (positive) - should be valid
            -0.01,  // Exactly at threshold (negative) - should be valid
            100.0,  // Very large positive
            -100.0, // Very large negative
        ];

        for avg_q_value in test_cases {
            // WHEN: Constraint check is performed
            let is_collapsed = is_q_value_collapsed(avg_q_value);

            // THEN: Should NOT be flagged (magnitude >= 0.01)
            assert!(
                !is_collapsed,
                "Q-value {} (|q| = {:.4} >= 0.01) should be VALID",
                avg_q_value,
                avg_q_value.abs()
            );
        }
    }

    #[test]
    fn test_boundary_conditions() {
        // GIVEN: Values exactly at the 0.01 threshold
        let valid_cases = vec![0.01, -0.01]; // Should be valid (|q| >= 0.01)
        let invalid_cases = vec![0.009, -0.009]; // Should be invalid (|q| < 0.01)

        // WHEN/THEN: Valid cases should NOT be flagged
        for avg_q_value in valid_cases {
            assert!(
                !is_q_value_collapsed(avg_q_value),
                "Q-value {} (|q| = {:.4}) at threshold should be VALID",
                avg_q_value,
                avg_q_value.abs()
            );
        }

        // WHEN/THEN: Invalid cases SHOULD be flagged
        for avg_q_value in invalid_cases {
            assert!(
                is_q_value_collapsed(avg_q_value),
                "Q-value {} (|q| = {:.4}) below threshold should be INVALID",
                avg_q_value,
                avg_q_value.abs()
            );
        }
    }
}