graph/db: expand AddChannelEdge test

Expand the existing TestAddChannelEdgeShellNodes test so that we have
coverage for error we expect when AddChannelEdge is called a second time
if we already know of a channel.

Author: ellemouton

graph/db/graph_test.go

@@ -3337,29 +3337,28 @@ func TestAddChannelEdgeShellNodes(t *testing.T) {
 	// To start, we'll create two nodes, and only add one of them to the
 	// channel graph.
 	node1 := createTestVertex(t)
-	if err := graph.AddLightningNode(node1); err != nil {
-		t.Fatalf("unable to add node: %v", err)
-	}
+	require.NoError(t, graph.SetSourceNode(node1))
 	node2 := createTestVertex(t)
 
 	// We'll now create an edge between the two nodes, as a result, node2
 	// should be inserted into the database as a shell node.
 	edgeInfo, _ := createEdge(100, 0, 0, 0, node1, node2)
-	if err := graph.AddChannelEdge(&edgeInfo); err != nil {
-		t.Fatalf("unable to add edge: %v", err)
-	}
+	require.NoError(t, graph.AddChannelEdge(&edgeInfo))
 
 	// Ensure that node1 was inserted as a full node, while node2 only has
 	// a shell node present.
 	node1, err := graph.FetchLightningNode(node1.PubKeyBytes)
 	require.NoError(t, err, "unable to fetch node1")
-	if !node1.HaveNodeAnnouncement {
-		t.Fatalf("have shell announcement for node1, shouldn't")
-	}
+	require.True(t, node1.HaveNodeAnnouncement)
 
 	node2, err = graph.FetchLightningNode(node2.PubKeyBytes)
 	require.NoError(t, err, "unable to fetch node2")
 	require.False(t, node2.HaveNodeAnnouncement)
+
+	// Show that attempting to add the channel again will result in an
+	// error.
+	err = graph.AddChannelEdge(&edgeInfo)
+	require.ErrorIs(t, err, ErrEdgeAlreadyExist)
 }
 
 // TestNodePruningUpdateIndexDeletion tests that once a node has been removed