Estimate fan duty from observed RPM maxima

audit/internal/platform/sat_fan_stress_test.go

@@ -1,6 +1,7 @@
 package platform
 
 import (
+	"path/filepath"
 	"testing"
 	"time"
 )
@@ -50,6 +51,53 @@ func TestParseFanDutyCyclePctSensorsJSON(t *testing.T) {
 	}
 }
 
+func TestEstimateFanDutyCyclePctFromObservation(t *testing.T) {
+	t.Parallel()
+
+	oldPath := fanObservationStatePath
+	oldState := fanObservation
+	oldInit := fanObservationInit
+	oldCandidates := fanPeakCandidates
+	fanObservationStatePath = filepath.Join(t.TempDir(), "fan-observation.json")
+	fanObservation = fanObservationState{}
+	fanObservationInit = false
+	fanPeakCandidates = make(map[string]fanPeakCandidate)
+	t.Cleanup(func() {
+		fanObservationStatePath = oldPath
+		fanObservation = oldState
+		fanObservationInit = oldInit
+		fanPeakCandidates = oldCandidates
+	})
+
+	start := time.Unix(100, 0)
+	updateFanObservation([]FanReading{{Name: "FAN1", RPM: 5000}}, start)
+	if _, ok := estimateFanDutyCyclePctFromObservation([]FanReading{{Name: "FAN1", RPM: 2500}}); ok {
+		t.Fatalf("single-sample spike should not establish observed max")
+	}
+
+	updateFanObservation([]FanReading{{Name: "FAN1", RPM: 5200}}, start.Add(500*time.Millisecond))
+	updateFanObservation([]FanReading{{Name: "FAN1", RPM: 5100}}, start.Add(1500*time.Millisecond))
+
+	got, ok := estimateFanDutyCyclePctFromObservation([]FanReading{{Name: "FAN1", RPM: 2600}})
+	if !ok {
+		t.Fatalf("expected estimated duty cycle from persisted observed max")
+	}
+	if got < 43 || got > 44 {
+		t.Fatalf("got=%v want ~43.3", got)
+	}
+
+	fanObservation = fanObservationState{}
+	fanObservationInit = false
+	fanPeakCandidates = make(map[string]fanPeakCandidate)
+	got, ok = estimateFanDutyCyclePctFromObservation([]FanReading{{Name: "FAN1", RPM: 2600}})
+	if !ok {
+		t.Fatalf("expected persisted observed max to be reloaded from disk")
+	}
+	if got < 43 || got > 44 {
+		t.Fatalf("reloaded got=%v want ~43.3", got)
+	}
+}
+
 func TestParseDCMIPowerReading(t *testing.T) {
 	raw := `
 Instantaneous power reading:                   512 Watts