Exercise dirname matches metadata exercise slug (exercism#774)

* Exercise dirname matches metadata exercise slug

* Avoid panic when err nil on test failure

* Make error message actionable

cmd/submit.go

@@ -141,6 +141,20 @@ func runSubmit(cfg config.Config, flags *pflag.FlagSet, args []string) error {
 		return err
 	}
 
+	if exercise.Slug != metadata.Exercise {
+		// TODO: error msg should suggest running future doctor command
+		msg := `
+
+	The exercise directory does not match exercise slug in metadata:
+
+		expected '%[1]s' but got '%[2]s'
+
+	Please rename the directory '%[1]s' to '%[2]s' and try again.
+
+		`
+		return fmt.Errorf(msg, exercise.Slug, metadata.Exercise)
+	}
+
 	if !metadata.IsRequester {
 		// TODO: add test
 		msg := `

cmd/submit_test.go

@@ -548,6 +548,40 @@ func TestSubmitRelativePath(t *testing.T) {
 	assert.Equal(t, "This is a file.", submittedFiles["file.txt"])
 }
 
+func TestExerciseDirnameMatchesMetadataSlug(t *testing.T) {
+	submittedFiles := map[string]string{}
+	ts := fakeSubmitServer(t, submittedFiles)
+	defer ts.Close()
+
+	tmpDir, err := ioutil.TempDir("", "submit-files")
+	defer os.RemoveAll(tmpDir)
+	assert.NoError(t, err)
+
+	dir := filepath.Join(tmpDir, "bogus-track", "bogus-exercise-doesnt-match-metadata-slug")
+	os.MkdirAll(filepath.Join(dir, "subdir"), os.FileMode(0755))
+	writeFakeMetadata(t, dir, "bogus-track", "bogus-exercise")
+
+	file1 := filepath.Join(dir, "file-1.txt")
+	err = ioutil.WriteFile(file1, []byte("This is file 1."), os.FileMode(0755))
+	assert.NoError(t, err)
+
+	v := viper.New()
+	v.Set("token", "abc123")
+	v.Set("workspace", tmpDir)
+	v.Set("apibaseurl", ts.URL)
+
+	cfg := config.Config{
+		Persister:       config.InMemoryPersister{},
+		Dir:             tmpDir,
+		UserViperConfig: v,
+	}
+
+	err = runSubmit(cfg, pflag.NewFlagSet("fake", pflag.PanicOnError), []string{file1})
+	if assert.Error(t, err) {
+		assert.Regexp(t, "directory does not match exercise slug", err.Error())
+	}
+}
+
 func writeFakeMetadata(t *testing.T, dir, trackID, exerciseSlug string) {
 	metadata := &workspace.ExerciseMetadata{
 		ID:          "bogus-solution-uuid",