remove os.Exit in magician subcommands (GoogleCloudPlatform#10901)

.ci/magician/cmd/generate_downstream.go

@@ -142,7 +142,7 @@ func execGenerateDownstream(baseBranch, command, repo, version, ref string, gh G
 	if commitErr != nil {
 		fmt.Println("Error creating commit: ", commitErr)
 		if !strings.Contains(commitErr.Error(), "nothing to commit") {
-			os.Exit(1)
+			return fmt.Errorf("error creating commit: %w", commitErr)
 		}
 	}
 

.ci/magician/cmd/scheduled_pr_reminders.go

@@ -63,8 +63,7 @@ var scheduledPrReminders = &cobra.Command{
 	RunE: func(cmd *cobra.Command, args []string) error {
 		githubToken, ok := os.LookupEnv("GITHUB_TOKEN")
 		if !ok {
-			fmt.Println("Did not provide GITHUB_TOKEN environment variable")
-			os.Exit(1)
+			return fmt.Errorf("did not provide GITHUB_TOKEN environment variable")
 		}
 		gh := github.NewClient(nil).WithAuthToken(githubToken)
 		return execScheduledPrReminders(gh)

.ci/magician/cmd/test_tgc_integration.go

@@ -34,7 +34,6 @@ var testTGCIntegrationCmd = &cobra.Command{
 		rnr, err := exec.NewRunner()
 		if err != nil {
 			return fmt.Errorf("error creating runner: %w", err)
-			os.Exit(1)
 		}
 
 		ctlr := source.NewController(goPath, "modular-magician", githubToken, rnr)

.ci/magician/cmd/wait_for_commit.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"magician/exec"
 	"magician/source"
-	"os"
 	"strings"
 	"time"
 
@@ -33,8 +32,7 @@ var waitForCommitCmd = &cobra.Command{
 
 		rnr, err := exec.NewRunner()
 		if err != nil {
-			fmt.Println("Error creating Runner: ", err)
-			os.Exit(1)
+			return fmt.Errorf("error creating Runner: %w", err)
 		}
 
 		return execWaitForCommit(syncBranchPrefix, baseBranch, sha, rnr)