fix: make TestDropNamespaceErr resilient to async namespace operations

DropAll and DropNamespace are asynchronous operations. The test was
flaky because it called ListNamespaces immediately after these
operations, before the state had propagated. Added polling helper
to wait for the expected namespace count.

Author: mlwelles

edgraph/namespace_test.go

@@ -10,13 +10,40 @@ package edgraph
 import (
 	"context"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
 
 	"github.com/dgraph-io/dgraph/v25/dgraphapi"
 	"github.com/dgraph-io/dgraph/v25/dgraphtest"
 )
 
+// waitForNamespaceCount polls ListNamespaces until the expected count is reached or timeout.
+// This is needed because DropAll and DropNamespace are asynchronous operations.
+func waitForNamespaceCount(t *testing.T, client *dgraphapi.GrpcClient, expected int, timeout time.Duration) {
+	t.Helper()
+	ctx := context.Background()
+	deadline := time.Now().Add(timeout)
+
+	for time.Now().Before(deadline) {
+		nsMaps, err := client.ListNamespaces(ctx)
+		if err != nil {
+			t.Logf("ListNamespaces error (will retry): %v", err)
+			time.Sleep(100 * time.Millisecond)
+			continue
+		}
+		if len(nsMaps) == expected {
+			return
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+
+	// Final check with assertion on timeout
+	nsMaps, err := client.ListNamespaces(ctx)
+	require.NoError(t, err)
+	require.Len(t, nsMaps, expected)
+}
+
 func TestNamespaces(t *testing.T) {
 	dc := dgraphtest.NewComposeCluster()
 	client, cleanup, err := dc.Client()
@@ -85,6 +112,9 @@ func TestDropNamespaceErr(t *testing.T) {
 		dgraphapi.DefaultUser, dgraphapi.DefaultPassword))
 	require.NoError(t, client.DropAll())
 
+	// Wait for DropAll to complete (async operation)
+	waitForNamespaceCount(t, client, 1, 30*time.Second)
+
 	// create ns1
 	ctx := context.Background()
 	ns1, err := client.CreateNamespace(ctx)
@@ -94,7 +124,6 @@ func TestDropNamespaceErr(t *testing.T) {
 	require.NoError(t, client.DropNamespace(ctx, ns1))
 	require.NoError(t, client.DropNamespace(ctx, uint64(10000000)))
 
-	nsMaps, err := client.ListNamespaces(ctx)
-	require.NoError(t, err)
-	require.Len(t, nsMaps, 1)
+	// Wait for DropNamespace to complete (async operation)
+	waitForNamespaceCount(t, client, 1, 30*time.Second)
 }