test: cover runtime indicator and document semantics

docs/API.md

@@ -43,6 +43,8 @@ Current transmitter status (read-only snapshot). Runtime indicator, alert, and q
 }
 ```
 
+`runtimeIndicator` is derived from the engine queue health plus any late buffers and can be "normal", "degraded", or "queueCritical". `runtimeAlert` surfaces a short reason (e.g. "queue health low" or "late buffers") when the indicator is not "normal", otherwise it stays empty.
+
 ---
 
 ### `GET /runtime`

internal/app/runtime_indicator_test.go

@@ -6,101 +6,55 @@ import (
 	"github.com/jan/fm-rds-tx/internal/output"
 )
 
-func TestRuntimeIndicator(t *testing.T) {
+func TestRuntimeIndicatorAndAlert(t *testing.T) {
 	cases := []struct {
-		name        string
-		queueHealth output.QueueHealth
-		lateBuffers uint64
-		want        RuntimeIndicator
+		name          string
+		health        output.QueueHealth
+		lateBuffers   uint64
+		wantIndicator RuntimeIndicator
+		wantAlert     string
 	}{
 		{
-			name:        "normal",
-			queueHealth: output.QueueHealthNormal,
-			lateBuffers: 0,
-			want:        RuntimeIndicatorNormal,
+			name:          "queue critical",
+			health:        output.QueueHealthCritical,
+			lateBuffers:   0,
+			wantIndicator: RuntimeIndicatorQueueCritical,
+			wantAlert:     "queue health critical",
 		},
 		{
-			name:        "degradedLateBuffers",
-			queueHealth: output.QueueHealthNormal,
-			lateBuffers: 1,
-			want:        RuntimeIndicatorDegraded,
+			name:          "queue low",
+			health:        output.QueueHealthLow,
+			lateBuffers:   0,
+			wantIndicator: RuntimeIndicatorDegraded,
+			wantAlert:     "queue health low",
 		},
 		{
-			name:        "degradedQueueLow",
-			queueHealth: output.QueueHealthLow,
-			lateBuffers: 0,
-			want:        RuntimeIndicatorDegraded,
+			name:          "late buffers",
+			health:        output.QueueHealthNormal,
+			lateBuffers:   2,
+			wantIndicator: RuntimeIndicatorDegraded,
+			wantAlert:     "late buffers",
 		},
 		{
-			name:        "queueCritical",
-			queueHealth: output.QueueHealthCritical,
-			lateBuffers: 0,
-			want:        RuntimeIndicatorQueueCritical,
-		},
-		{
-			name:        "criticalLateBuffers",
-			queueHealth: output.QueueHealthCritical,
-			lateBuffers: 3,
-			want:        RuntimeIndicatorQueueCritical,
+			name:          "normal",
+			health:        output.QueueHealthNormal,
+			lateBuffers:   0,
+			wantIndicator: RuntimeIndicatorNormal,
+			wantAlert:     "",
 		},
 	}
 
 	for _, tc := range cases {
 		tc := tc
 		t.Run(tc.name, func(t *testing.T) {
-			if got := runtimeIndicator(tc.queueHealth, tc.lateBuffers); got != tc.want {
-				t.Fatalf("runtime indicator mismatch: queue=%s late=%d want=%s got=%s",
-					tc.queueHealth, tc.lateBuffers, tc.want, got)
+			t.Parallel()
+			got := runtimeIndicator(tc.health, tc.lateBuffers)
+			if got != tc.wantIndicator {
+				t.Fatalf("indicator: expected %s, got %s", tc.wantIndicator, got)
 			}
-		})
-	}
-}
-
-func TestRuntimeAlert(t *testing.T) {
-	cases := []struct {
-		name        string
-		queueHealth output.QueueHealth
-		lateBuffers uint64
-		want        string
-	}{
-		{
-			name:        "normal",
-			queueHealth: output.QueueHealthNormal,
-			lateBuffers: 0,
-			want:        "",
-		},
-		{
-			name:        "lateBuffers",
-			queueHealth: output.QueueHealthNormal,
-			lateBuffers: 1,
-			want:        "late buffers",
-		},
-		{
-			name:        "queueLow",
-			queueHealth: output.QueueHealthLow,
-			lateBuffers: 0,
-			want:        "queue health low",
-		},
-		{
-			name:        "queueCritical",
-			queueHealth: output.QueueHealthCritical,
-			lateBuffers: 0,
-			want:        "queue health critical",
-		},
-		{
-			name:        "criticalLateBuffers",
-			queueHealth: output.QueueHealthCritical,
-			lateBuffers: 5,
-			want:        "queue health critical",
-		},
-	}
-
-	for _, tc := range cases {
-		tc := tc
-		t.Run(tc.name, func(t *testing.T) {
-			if got := runtimeAlert(tc.queueHealth, tc.lateBuffers); got != tc.want {
-				t.Fatalf("runtime alert mismatch: queue=%s late=%d want=%q got=%q",
-					tc.queueHealth, tc.lateBuffers, tc.want, got)
+			alert := runtimeAlert(tc.health, tc.lateBuffers)
+			if alert != tc.wantAlert {
+				t.Fatalf("alert: expected %q, got %q", tc.wantAlert, alert)
 			}
 		})
 	}