tapgarden: wait for asset registration in TestBookAssetSyncer

Update TestBookAssetSyncer to wait until the asset is registered with
the address book. This reduces test flakiness and improves reliability
of the unit tests.

Author: ffranr

tapgarden/custodian_test.go

@@ -584,12 +584,28 @@ func TestBookAssetSyncer(t *testing.T) {
 	// If we add the asset to the asset syncer, address creation should
 	// succeed.
 	h.syncer.AddAsset(*newAsset)
-	addrVersion = test.RandFlip(address.V0, address.V1)
-	newAddr, err := h.addrBook.NewAddress(
-		ctx, addrVersion, newAsset.ID(), 1, nil, proofCourierAddr,
-	)
+
+	// Fetch the asset from the syncer. This should trigger the
+	// background goroutine to add the asset to the address book.
+	_, err = h.syncer.FetchAsset(newAsset.ID())
 	require.NoError(t, err)
-	require.NotNil(t, newAddr)
+
+	// Eventually, the asset should be registered and we should be able to
+	// create a new address for it.
+	var newAddr *address.AddrWithKeyInfo
+	addrVersion = test.RandFlip(address.V0, address.V1)
+
+	require.Eventually(t, func() bool {
+		newAddr, err = h.addrBook.NewAddress(
+			ctx, addrVersion, newAsset.ID(), 1, nil,
+			proofCourierAddr,
+		)
+		if err != nil {
+			return false
+		}
+
+		return newAddr != nil
+	}, defaultTimeout, wait.PollInterval)
 
 	h.keyRing.AssertNumberOfCalls(t, "DeriveNextTaprootAssetKey", 2)