Add stub for validate test

command/test-fixtures/validate/template.json

+{
+  "builders":[
+    {
+      "type":"file",
+      "target":"chocolate.txt",
+      "content":"chocolate"
+    }
+  ],
+  "min_packer_version":"0.8.0"
+}

command/validate_test.go

+package command
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+func TestValidateCommand(t *testing.T) {
+	c := &ValidateCommand{
+		Meta: testMetaFile(t),
+	}
+
+	args := []string{
+		filepath.Join(testFixture("validate"), "template.json"),
+	}
+
+	defer cleanup()
+
+	if code := c.Run(args); code != 0 {
+		fatalCommand(t, c.Meta)
+	}
+
+	if !fileExists("chocolate.txt") {
+		t.Error("Expected to find chocolate.txt")
+	}
+	if !fileExists("vanilla.txt") {
+		t.Error("Expected to find vanilla.txt")
+	}
+	if fileExists("cherry.txt") {
+		t.Error("Expected NOT to find cherry.txt")
+	}
+}