packer: Default cache is just to os temporary dir

packer/environment.go

@@ -104,6 +104,11 @@ func NewEnvironment(config *EnvironmentConfig) (resultEnv Environment, err error
 		env.components.Provisioner = func(string) (Provisioner, error) { return nil, nil }
 	}
 
+	// The default cache is just the system temporary directory
+	if env.cache == nil {
+		env.cache = &FileCache{CacheDir: os.TempDir()}
+	}
+
 	resultEnv = env
 	return
 }

packer/environment_test.go

@@ -111,6 +111,14 @@ func TestEnvironment_Builder_Error(t *testing.T) {
 	assert.Nil(returnedBuilder, "should be no builder")
 }
 
+func TestEnvironment_Cache(t *testing.T) {
+	config := DefaultEnvironmentConfig()
+	env, _ := NewEnvironment(config)
+	if env.Cache() == nil {
+		t.Fatal("cache should not be nil")
+	}
+}
+
 func TestEnvironment_Cli_Error(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)