Fail early if chart or release is missing

README.md

@@ -8,7 +8,7 @@ TODO:
 * [x] Make `golint` part of the build process (and make it pass)
 * [x] Implement debug output
 * [x] Flesh out `helm upgrade` until it's capable of working
-* [ ] Implement config settings for `upgrade`
+* [x] Implement config settings for `upgrade`
 * [ ] Implement `helm lint`
 * [ ] Implement `helm delete`
 * [ ] EKS support

internal/run/upgrade.go

@@ -26,6 +26,13 @@ func (u *Upgrade) Execute(_ Config) error {
 
 // Prepare gets the Upgrade ready to execute.
 func (u *Upgrade) Prepare(cfg Config) error {
+	if u.Chart == "" {
+		return fmt.Errorf("chart is required")
+	}
+	if u.Release == "" {
+		return fmt.Errorf("release is required")
+	}
+
 	args := []string{"--kubeconfig", cfg.KubeConfig}
 
 	if cfg.Namespace != "" {

internal/run/upgrade_test.go

@@ -136,6 +136,26 @@ func (suite *UpgradeTestSuite) TestPrepareWithUpgradeFlags() {
 	suite.Require().Nil(err)
 }
 
+func (suite *UpgradeTestSuite) TestRequiresChartAndRelease() {
+	// These aren't really expected, but allowing them gives clearer test-failure messages
+	suite.mockCmd.EXPECT().Stdout(gomock.Any()).AnyTimes()
+	suite.mockCmd.EXPECT().Stderr(gomock.Any()).AnyTimes()
+
+	u := Upgrade{
+		Release: "seth_everman_unskippable_cutscene",
+	}
+
+	err := u.Prepare(Config{})
+	suite.EqualError(err, "chart is required", "Chart should be mandatory")
+
+	u = Upgrade{
+		Chart: "billboard_top_zero",
+	}
+
+	err = u.Prepare(Config{})
+	suite.EqualError(err, "release is required", "Release should be mandatory")
+}
+
 func (suite *UpgradeTestSuite) TestPrepareDebugFlag() {
 	u := Upgrade{
 		Chart:   "at40",