Added Prepare tests around formula URLs

Signed-off-by: Andrew Cornies <acornies@gmail.com>

provisioner/salt-masterless/provisioner.go

@@ -363,7 +363,7 @@ func (p *Provisioner) Provision(ctx context.Context, ui packer.Ui, comm packer.C
 		for _, f := range formulas {
 			if _, err := os.Stat(f); !os.IsNotExist(err) && f != p.config.LocalStateTree {
 				ui.Message(fmt.Sprintf("Removing Salt formula: %s", f))
-				os.RemoveAll(f)
+				defer os.RemoveAll(f)
 			}
 		}
 	}

provisioner/salt-masterless/provisioner_test.go

@@ -325,3 +325,33 @@ func TestProvisionerPrepare_GuestOSType(t *testing.T) {
 		t.Fatalf("GuestOSType should be 'windows'")
 	}
 }
+
+func TestProvisionerPrepare_BadFormulaURL(t *testing.T) {
+	var p Provisioner
+	config := testConfig()
+
+	config["formulas"] = []string{
+		"git::https://github.com/org/some-formula.git//",
+	}
+
+	err := p.Prepare(config)
+	if err == nil {
+		t.Fatalf("Expected invalid formula URL: %s", err)
+	}
+}
+
+func TestProvisionerPrepare_ValidFormulaURLs(t *testing.T) {
+
+	var p Provisioner
+	config := testConfig()
+
+	config["formulas"] = []string{
+		"git::https://github.com/org/some-formula.git//example",
+		"git@github.com:org/some-formula.git//example",
+	}
+
+	err := p.Prepare(config)
+	if err != nil {
+		t.Fatalf("Unexpected error in formula URLs: %s", err)
+	}
+}