Harden audio meter regression coverage

src/correlation.rs

@@ -145,6 +145,26 @@ mod tests {
         assert_eq!(fast.negative_peak(), 0.0);
     }
 
+    #[test]
+    fn fast_response_tracks_a_phase_reversal_before_slow_response() {
+        let sample_rate = 48_000;
+        let mut fast = CorrelationMeter::new(sample_rate, 1.0, 0);
+        let mut slow = CorrelationMeter::new(sample_rate, 2.5, 0);
+        for index in 0..sample_rate as usize * 5 {
+            let sample = if index & 1 == 0 { 0.5 } else { -0.5 };
+            fast.process(sample, sample);
+            slow.process(sample, sample);
+        }
+        for index in 0..sample_rate as usize {
+            let sample = if index & 1 == 0 { 0.5 } else { -0.5 };
+            fast.process(sample, -sample);
+            slow.process(sample, -sample);
+        }
+        assert!(fast.value() < slow.value() - 0.35);
+        assert!(fast.negative_peak() < 0.0);
+        assert_eq!(slow.negative_peak(), 0.0);
+    }
+
     #[test]
     fn silence_and_single_channel_are_neutral() {
         let mut meter = CorrelationMeter::new(48_000, 1.0, 0);