Add tracing and relevant tests (#21)

* Add tracing and relevant tests.

* fixup! Add tracing and relevant tests.

* gofmt the code 🤷

* fixup! gofmt the code 🤷

tracing/tracing_test.go

@@ -0,0 +1,102 @@
+package tracing
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"go.opentelemetry.io/otel/trace"
+)
+
+func TestParseTraceHeader(t *testing.T) {
+	tests := []struct {
+		name    string
+		header  string
+		want    *TraceSpanInfo
+		wantErr bool
+	}{
+		{
+			name:   "valid trace header",
+			header: `{"traceparent": "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01"}`,
+			want: &TraceSpanInfo{
+				TraceParent: "00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01",
+			},
+			wantErr: false,
+		},
+		{
+			name:    "invalid json",
+			header:  `{"traceparent": invalid}`,
+			want:    nil,
+			wantErr: true,
+		},
+		{
+			name:    "empty header",
+			header:  "",
+			want:    nil,
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ParseTraceHeader(tt.header)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("ParseTraceHeader() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if !tt.wantErr {
+				gotJSON, _ := json.Marshal(got)
+				wantJSON, _ := json.Marshal(tt.want)
+				if string(gotJSON) != string(wantJSON) {
+					t.Errorf("ParseTraceHeader() = %v, want %v", string(gotJSON), string(wantJSON))
+				}
+			}
+		})
+	}
+}
+
+func TestNewTracing(t *testing.T) {
+	// Skip actual connection tests since they require a running collector
+	t.Run("empty endpoint", func(t *testing.T) {
+		ctx := context.Background()
+		_, err := NewTracing(ctx, "")
+		assert.Error(t, err, "Expected error for empty endpoint")
+		assert.Contains(t, err.Error(), "endpoint cannot be empty")
+	})
+
+	t.Run("nil context", func(t *testing.T) {
+		_, err := NewTracing(nil, "localhost:4317")
+		assert.Error(t, err, "Expected error for nil context")
+		assert.Contains(t, err.Error(), "context cannot be nil")
+	})
+}
+
+func TestTracingSetup_ExtractSpanContext(t *testing.T) {
+	ts := &TracingSetup{}
+	spanInfo := &TraceSpanInfo{
+		TraceParent: "invalid-traceparent",
+	}
+
+	_, err := ts.ExtractSpanContext(spanInfo)
+	assert.Error(t, err, "Expected error for invalid traceparent")
+	assert.Contains(t, err.Error(), "invalid span context")
+}
+
+func TestTracingSetup_StartSpan(t *testing.T) {
+	ts := &TracingSetup{}
+	ctx := context.Background()
+
+	span, newCtx := ts.StartSpan(ctx, "test-span")
+	assert.NotNil(t, span, "Expected non-nil span even when tracer is nil")
+	assert.NotNil(t, newCtx, "Expected non-nil context")
+	assert.Equal(t, trace.SpanFromContext(ctx), span, "Expected span from context when tracer is nil")
+}
+
+func TestTracingSetup_Shutdown(t *testing.T) {
+	ts := &TracingSetup{}
+	ctx := context.Background()
+
+	err := ts.Shutdown(ctx)
+	assert.NoError(t, err, "Expected no error when shutting down nil tracer provider")
+}