Magician vcr eap (#12547)

Author: trodge

.ci/magician/cmd/interfaces.go

@@ -48,6 +48,7 @@ type ExecRunner interface {
 	RemoveAll(path string) error
 	PushDir(path string) error
 	PopDir() error
+	ReadFile(name string) (string, error)
 	WriteFile(name, data string) error
 	AppendFile(name, data string) error // Not used (yet).
 	Run(name string, args []string, env map[string]string) (string, error)

.ci/magician/cmd/test_eap_vcr.go

@@ -104,9 +104,9 @@ func execTestEAPVCR(changeNumber, genPath, kokoroArtifactsDir, modifiedFilePath
 		return fmt.Errorf("error changing to gen path: %w", err)
 	}
 
-	changedFiles, err := rnr.Run("git", []string{"diff", "--name-only"}, nil)
+	changedFiles, err := rnr.ReadFile("diff.log")
 	if err != nil {
-		return fmt.Errorf("error diffing gen path: %w", err)
+		return fmt.Errorf("error reading diff log: %w", err)
 	}
 
 	services, runFullVCR := modifiedPackages(strings.Split(changedFiles, "\n"), provider.Private)