cmd/callgraph: add test of -algo=vta

This should have been included in
https://go-review.googlesource.com/c/tools/+/410138

Change-Id: Ic8a4f1b5dbcdb320fb872b24484b830dcb56fd41
Reviewed-on: https://go-review.googlesource.com/c/tools/+/410123
Run-TryBot: Alan Donovan <adonovan@google.com>
Reviewed-by: Tim King <taking@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Zvonimir Pavlinovic <zpavlinovic@google.com>

cmd/callgraph/main_test.go

@@ -59,6 +59,12 @@ func TestCallgraph(t *testing.T) {
 			`pkg.main2 --> (pkg.C).f`,
 			`pkg.main2 --> (pkg.D).f`,
 		}},
+		{"vta", false, []string{
+			// vta distinguishes main->C, main2->D.
+			"pkg.main --> (pkg.C).f",
+			"pkg.main --> pkg.main2",
+			"pkg.main2 --> (pkg.D).f",
+		}},
 		{"pta", false, []string{
 			// pta distinguishes main->C, main2->D.  Also has a root node.
 			`<root> --> pkg.init`,
@@ -75,6 +81,12 @@ func TestCallgraph(t *testing.T) {
 			`pkg.Example --> (pkg.C).f`,
 			`pkg.main --> (pkg.C).f`,
 		}},
+		{"vta", true, []string{
+			`pkg.test.main --> testing.MainStart`,
+			`testing.runExample --> pkg.Example`,
+			`pkg.Example --> (pkg.C).f`,
+			`pkg.main --> (pkg.C).f`,
+		}},
 		{"pta", true, []string{
 			`<root> --> pkg.test.main`,
 			`<root> --> pkg.main`,
@@ -95,13 +107,15 @@ func TestCallgraph(t *testing.T) {
 		for _, line := range strings.Split(fmt.Sprint(stdout), "\n") {
 			edges[line] = true
 		}
+		ok := true
 		for _, edge := range test.want {
 			if !edges[edge] {
+				ok = false
 				t.Errorf("callgraph(%q, %t): missing edge: %s",
 					test.algo, test.tests, edge)
 			}
 		}
-		if t.Failed() {
+		if !ok {
 			t.Log("got:\n", stdout)
 		}
 	}