lang: Avoid running graphviz in tests by default

This will help travis actually run the tests faster.

lang/interpret_test.go

@@ -40,6 +40,10 @@ import (
 	"github.com/spf13/afero"
 )
 
+const (
+	runGraphviz = false // run graphviz in tests?
+)
+
 func vertexAstCmpFn(v1, v2 pgraph.Vertex) (bool, error) {
 	//fmt.Printf("V1: %T %+v\n", v1, v1)
 	//node := v1.(*funcs.Node)
@@ -902,12 +906,14 @@ func TestAstFunc1(t *testing.T) {
 					t.Logf("test #%d: edge(%+v): %+v -> %+v", index, e, v1, v2)
 				}
 			}
+			if runGraphviz {
 				t.Logf("test #%d: Running graphviz...", index)
 				if err := graph.ExecGraphviz("dot", "/tmp/graphviz.dot", ""); err != nil {
 					t.Errorf("test #%d: FAIL", index)
 					t.Errorf("test #%d: writing graph failed: %+v", index, err)
 					return
 				}
+			}
 
 			str := strings.Trim(graph.Sprint(), "\n") // text format of graph
 			if expstr == magicEmpty {
@@ -1334,12 +1340,15 @@ func TestAstFunc2(t *testing.T) {
 					t.Logf("test #%d: edge(%+v): %+v -> %+v", index, e, v1, v2)
 				}
 			}
+
+			if runGraphviz {
 				t.Logf("test #%d: Running graphviz...", index)
 				if err := graph.ExecGraphviz("dot", "/tmp/graphviz.dot", ""); err != nil {
 					t.Errorf("test #%d: FAIL", index)
 					t.Errorf("test #%d: writing graph failed: %+v", index, err)
 					return
 				}
+			}
 
 			// run the function engine once to get some real output
 			funcs := &funcs.Engine{