depgraph: add Noun function to get a noun

depgraph/graph.go

@@ -109,6 +109,17 @@ func (g *Graph) CheckConstraints() error {
 	return nil
 }
 
+// Noun returns the noun with the given name, or nil if it cannot be found.
+func (g *Graph) Noun(name string) *Noun {
+	for _, n := range g.Nouns {
+		if n.Name == name {
+			return n
+		}
+	}
+
+	return nil
+}
+
 // String generates a little ASCII string of the graph, useful in
 // debugging output.
 func (g *Graph) String() string {

depgraph/graph_test.go

@@ -55,6 +55,28 @@ func NounMapToList(m map[string]*Noun) []*Noun {
 	return list
 }
 
+func TestGraph_Noun(t *testing.T) {
+	nodes := ParseNouns(`a -> b
+a -> c
+b -> d
+b -> e
+c -> d
+c -> e`)
+
+	g := &Graph{
+		Name:  "Test",
+		Nouns: NounMapToList(nodes),
+	}
+
+	n := g.Noun("a")
+	if n == nil {
+		t.Fatal("should not be nil")
+	}
+	if n.Name != "a" {
+		t.Fatalf("bad: %#v", n)
+	}
+}
+
 func TestGraph_String(t *testing.T) {
 	nodes := ParseNouns(`a -> b
 a -> c