client/v3/watch_test.go: test fmt metadata print

Signed-off-by: Mohamed Awnallah <mohamedmohey2352@gmail.com>
Co-authored-by: Benjamin Wang <ahrtr>

clientv3/watch_test.go

@@ -15,9 +15,12 @@
 package clientv3
 
 import (
+	"context"
 	"testing"
 
-	"go.etcd.io/etcd/mvcc/mvccpb"
+	"google.golang.org/grpc/metadata"
+
+	"go.etcd.io/etcd/api/v3/mvccpb"
 )
 
 func TestEvent(t *testing.T) {
@@ -53,3 +56,53 @@ func TestEvent(t *testing.T) {
 		}
 	}
 }
+
+// TestStreamKeyFromCtx tests the streamKeyFromCtx function to ensure it correctly
+// formats metadata as a map[string][]string when extracting metadata from the context.
+//
+// The fmt package in Go guarantees that maps are printed in a consistent order,
+// sorted by the keys. This test verifies that the streamKeyFromCtx function
+// produces the expected formatted string representation of metadata maps when called with
+// various context scenarios.
+func TestStreamKeyFromCtx(t *testing.T) {
+	tests := []struct {
+		name     string
+		ctx      context.Context
+		expected string
+	}{
+		{
+			name: "multiple keys",
+			ctx: metadata.NewOutgoingContext(context.Background(), metadata.MD{
+				"key1": []string{"value1"},
+				"key2": []string{"value2a", "value2b"},
+			}),
+			expected: "map[key1:[value1] key2:[value2a value2b]]",
+		},
+		{
+			name:     "no keys",
+			ctx:      metadata.NewOutgoingContext(context.Background(), metadata.MD{}),
+			expected: "map[]",
+		},
+		{
+			name: "only one key",
+			ctx: metadata.NewOutgoingContext(context.Background(), metadata.MD{
+				"key1": []string{"value1", "value1a"},
+			}),
+			expected: "map[key1:[value1 value1a]]",
+		},
+		{
+			name:     "no metadata",
+			ctx:      context.Background(),
+			expected: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			actual := streamKeyFromCtx(tt.ctx)
+			if actual != tt.expected {
+				t.Errorf("streamKeyFromCtx() = %v, expected %v", actual, tt.expected)
+			}
+		})
+	}
+}