feat: ensure relative WorkingDir work

Currently the default WorkingDir in test is "/", while in reallife it's
empty.

This change the tests to reflect reel life and fix the case where
First WorkingDir is relative.

pkg/commands/workdir.go

@@ -48,7 +48,11 @@ func (w *WorkdirCommand) ExecuteCommand(config *v1.Config, buildArgs *dockerfile
 	if filepath.IsAbs(resolvedWorkingDir) {
 		config.WorkingDir = resolvedWorkingDir
 	} else {
-		config.WorkingDir = filepath.Join(config.WorkingDir, resolvedWorkingDir)
+		if config.WorkingDir != "" {
+			config.WorkingDir = filepath.Join(config.WorkingDir, resolvedWorkingDir)
+		} else {
+			config.WorkingDir = filepath.Join("/", resolvedWorkingDir)
+		}
 	}
 	logrus.Infof("Changed working directory to %s", config.WorkingDir)
 

pkg/commands/workdir_test.go

@@ -35,6 +35,11 @@ var workdirTests = []struct {
 	expectedPath  string
 	snapshotFiles []string
 }{
+	{
+		path:          "a",
+		expectedPath:  "/a",
+		snapshotFiles: []string{"/a"},
+	},
 	{
 		path:          "/a",
 		expectedPath:  "/a",
@@ -92,7 +97,7 @@ func TestWorkdirCommand(t *testing.T) {
 	}()
 
 	cfg := &v1.Config{
-		WorkingDir: "/",
+		WorkingDir: "",
 		Env: []string{
 			"path=usr/",
 			"home=/root",