pgraph: Filter graph should not include unfiltered vertices

This adds a test for another sneaky aspect of filter graph: It should
not pull in a vertex because another across the edge was included. If we
want this behaviour, then we need a different function or a config
option for this filter function.

pgraph/pgraph.go

@@ -512,7 +512,7 @@ func (g *Graph) FilterGraph(name string, vertices []Vertex) (*Graph, error) {
 		}
 		for k2, e := range x {
 			//log.Printf("Filter: %s -> %s # %s", k1.Name, k2.Name, e.Name)
-			if contains || VertexContains(k2, vertices) {
+			if contains && VertexContains(k2, vertices) {
 				newGraph.AddEdge(k1, k2, e)
 			}
 		}
@@ -538,7 +538,8 @@ func (g *Graph) DisconnectedGraphs() ([]*Graph, error) {
 		// dfs through the graph
 		dfs := g.DFS(start)
 		// filter all the collected elements into a new graph
-		newgraph, err := g.FilterGraph(g.Name, dfs)
+		// TODO: is this method of filtering correct here? && or || ?
+		newGraph, err := g.FilterGraph(g.Name, dfs)
 		if err != nil {
 			return nil, errwrap.Wrapf(err, "could not run DisconnectedGraphs() properly")
 		}
@@ -546,7 +547,7 @@ func (g *Graph) DisconnectedGraphs() ([]*Graph, error) {
 		d = append(d, dfs...) // extend
 
 		// append this new graph to the list
-		graphs = append(graphs, newgraph)
+		graphs = append(graphs, newGraph)
 
 		// if we've found all the elements, then we're done
 		// otherwise loop through to continue...

pgraph/pgraph_test.go

@@ -213,6 +213,33 @@ func TestFilterGraph2(t *testing.T) {
 	}
 }
 
+func TestFilterGraph3(t *testing.T) {
+	G, _ := NewGraph("g5")
+	v1 := NV("v1")
+	v2 := NV("v2")
+	v3 := NV("v3")
+	v4 := NV("v4")
+	v5 := NV("v5")
+	e1 := NE("e1")
+	e2 := NE("e2")
+	G.AddEdge(v1, v2, e1)
+	G.AddEdge(v3, v4, e2)
+	G.AddVertex(v5)
+
+	save := []Vertex{v1, v2, v3}
+	out, err := G.FilterGraph("new g5", save)
+	if err != nil {
+		t.Errorf("failed with: %v", err)
+	}
+
+	if c, i := len(save), out.NumVertices(); c != i {
+		t.Errorf("should have %d vertices instead of: %d", c, i)
+	}
+	if c, i := 1, out.NumEdges(); c != i {
+		t.Errorf("should have %d edges instead of: %d", c, i)
+	}
+}
+
 func TestDisconnectedGraphs1(t *testing.T) {
 	G, _ := NewGraph("g6")
 	v1 := NV("v1")