Fix tracing module's Jaeger sampling flag

js/modules/k6/experimental/tracing/propagator.go

@@ -69,11 +69,11 @@ const (
 	// "0 value is valid and means “root span” (when not ignored)"
 	JaegerRootSpanID = "0"
 
-	// JaegerSampledTraceFlag is the trace-flag value for an unsampled trace.
-	JaegerSampledTraceFlag = "0"
+	// JaegerUnsampledTraceFlag is the trace-flag value for an unsampled trace.
+	JaegerUnsampledTraceFlag = "0"
 
-	// JaegerUnsampledTraceFlag is the trace-flag value for a sampled trace.
-	JaegerUnsampledTraceFlag = "1"
+	// JaegerSampledTraceFlag is the trace-flag value for a sampled trace.
+	JaegerSampledTraceFlag = "1"
 )
 
 // JaegerPropagator is a Propagator for the Jaeger trace context header

js/modules/k6/experimental/tracing/propagator_test.go

@@ -0,0 +1,112 @@
+package tracing
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPropagate(t *testing.T) {
+	t.Parallel()
+
+	traceID := "abc123"
+
+	t.Run("W3C Propagator", func(t *testing.T) {
+		t.Parallel()
+
+		sampler := mockSampler{decision: true}
+		propagator := NewW3CPropagator(sampler)
+
+		gotHeader, gotErr := propagator.Propagate(traceID)
+
+		assert.NoError(t, gotErr)
+		assert.Contains(t, gotHeader, W3CHeaderName)
+
+		//nolint:staticcheck // as traceparent is not a canonical header
+		headerContent := gotHeader[W3CHeaderName][0]
+		assert.True(t, strings.HasPrefix(headerContent, W3CVersion+"-"+traceID+"-"))
+	})
+
+	t.Run("W3C propagator with sampled trace", func(t *testing.T) {
+		t.Parallel()
+
+		sampler := mockSampler{decision: true}
+		propagator := NewW3CPropagator(sampler)
+
+		gotHeader, gotErr := propagator.Propagate(traceID)
+		require.NoError(t, gotErr)
+		require.Contains(t, gotHeader, W3CHeaderName)
+
+		//nolint:staticcheck // as traceparent is not a canonical header
+		assert.True(t, strings.HasSuffix(gotHeader[W3CHeaderName][0], "-01"))
+	})
+
+	t.Run("W3C propagator with unsampled trace", func(t *testing.T) {
+		t.Parallel()
+
+		sampler := mockSampler{decision: false}
+		propagator := NewW3CPropagator(sampler)
+
+		gotHeader, gotErr := propagator.Propagate(traceID)
+		require.NoError(t, gotErr)
+		require.Contains(t, gotHeader, W3CHeaderName)
+
+		//nolint:staticcheck // as traceparent is not a canonical header
+		assert.True(t, strings.HasSuffix(gotHeader[W3CHeaderName][0], "-00"))
+	})
+
+	t.Run("Jaeger Propagator", func(t *testing.T) {
+		t.Parallel()
+
+		sampler := mockSampler{decision: true}
+		propagator := NewJaegerPropagator(sampler)
+
+		gotHeader, gotErr := propagator.Propagate(traceID)
+
+		assert.NoError(t, gotErr)
+		assert.Contains(t, gotHeader, JaegerHeaderName)
+
+		//nolint:staticcheck // as traceparent is not a canonical header
+		headerContent := gotHeader[JaegerHeaderName][0]
+		assert.True(t, strings.HasPrefix(headerContent, traceID+":"))
+		assert.True(t, strings.HasSuffix(headerContent, ":0:1"))
+	})
+
+	t.Run("Jaeger propagator with sampled trace", func(t *testing.T) {
+		t.Parallel()
+
+		sampler := mockSampler{decision: true}
+		propagator := NewJaegerPropagator(sampler)
+
+		gotHeader, gotErr := propagator.Propagate(traceID)
+		require.NoError(t, gotErr)
+		require.Contains(t, gotHeader, JaegerHeaderName)
+
+		//nolint:staticcheck // as traceparent is not a canonical header
+		assert.True(t, strings.HasSuffix(gotHeader[JaegerHeaderName][0], ":1"))
+	})
+
+	t.Run("Jaeger propagator with unsampled trace", func(t *testing.T) {
+		t.Parallel()
+
+		sampler := mockSampler{decision: false}
+		propagator := NewJaegerPropagator(sampler)
+
+		gotHeader, gotErr := propagator.Propagate(traceID)
+		require.NoError(t, gotErr)
+		require.Contains(t, gotHeader, JaegerHeaderName)
+
+		//nolint:staticcheck // as traceparent is not a canonical header
+		assert.True(t, strings.HasSuffix(gotHeader[JaegerHeaderName][0], ":0"))
+	})
+}
+
+type mockSampler struct {
+	decision bool
+}
+
+func (m mockSampler) ShouldSample() bool {
+	return m.decision
+}