test(otel): guard OTEL_TRACES_SAMPLER is honored

pkg/gotenberg/internal/otel/otel_test.go

@@ -0,0 +1,42 @@
+package otel
+
+import (
+	"context"
+	"log/slog"
+	"testing"
+
+	"go.opentelemetry.io/otel"
+)
+
+// TestInitTracerProvider_HonorsSamplerEnv guards the contract that the tracer
+// provider keeps honoring OTEL_TRACES_SAMPLER. The SDK reads it only when no
+// explicit sampler is configured, so any future WithSampler() would silently
+// break operator-side sampling control.
+func TestInitTracerProvider_HonorsSamplerEnv(t *testing.T) {
+	for _, tc := range []struct {
+		name        string
+		sampler     string
+		wantSampled bool
+	}{
+		{"always off", "always_off", false},
+		{"always on", "always_on", true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Setenv("OTEL_TRACES_EXPORTER", "none")
+			t.Setenv("OTEL_TRACES_SAMPLER", tc.sampler)
+
+			shutdown, err := InitTracerProvider(slog.New(slog.DiscardHandler), "test", "v0.0.0")
+			if err != nil {
+				t.Fatalf("init tracer provider: %v", err)
+			}
+			t.Cleanup(func() { _ = shutdown(context.Background()) })
+
+			_, span := otel.Tracer("test").Start(context.Background(), "span")
+			span.End()
+
+			if got := span.SpanContext().IsSampled(); got != tc.wantSampled {
+				t.Errorf("OTEL_TRACES_SAMPLER=%q: IsSampled() = %v, want %v", tc.sampler, got, tc.wantSampled)
+			}
+		})
+	}
+}