handling case no file to convert

app/converter/converter.go

@@ -19,6 +19,14 @@ type Converter struct {
 	workingDir string
 }
 
+type noFileToConvertError struct{}
+
+const noFileToConvertErrorMessage = "No file to convert"
+
+func (e *noFileToConvertError) Error() string {
+	return noFileToConvertErrorMessage
+}
+
 // NewConverter instantiates a converter by parsing a request.
 func NewConverter(r *http.Request) (*Converter, error) {
 	c := &Converter{
@@ -53,6 +61,10 @@ func NewConverter(r *http.Request) (*Converter, error) {
 		c.files = append(c.files, f)
 	}
 
+	if len(c.files) == 0 {
+		return c, &noFileToConvertError{}
+	}
+
 	return c, nil
 }
 

app/converter/converter_test.go

@@ -21,13 +21,18 @@ func makeRequest(filesPaths ...string) *http.Request {
 		var part io.Writer
 		defer w.Close()
 
-		for _, filePath := range filesPaths {
+		if len(filesPaths) == 0 {
-			file, _ := os.Open(filePath)
+			part, _ = mpw.CreateFormField("foo")
-			defer file.Close()
+			part.Write([]byte("bar"))
+		} else {
+			for _, filePath := range filesPaths {
+				file, _ := os.Open(filePath)
+				defer file.Close()
 
-			fileInfo, _ := file.Stat()
+				fileInfo, _ := file.Stat()
-			part, _ = mpw.CreateFormFile("files", fileInfo.Name())
+				part, _ = mpw.CreateFormFile("files", fileInfo.Name())
-			io.Copy(part, file)
+				io.Copy(part, file)
+			}
 		}
 
 		mpw.Close()
@@ -64,6 +69,11 @@ func TestNewConverter(t *testing.T) {
 	if _, err := NewConverter(makeRequest(oPath, path)); err == nil {
 		t.Error("Converter should not have been instantiated!")
 	}
+
+	// case 5: uses a request with no file.
+	if _, err := NewConverter(makeRequest()); err == nil {
+		t.Error("Converter should not have been instantiated!")
+	}
 }
 
 func TestConvert(t *testing.T) {
@@ -115,3 +125,11 @@ func TestClear(t *testing.T) {
 		t.Error("Converter should have been able to clear itself!")
 	}
 }
+
+func TestNoFileToConvertError(t *testing.T) {
+	err := &noFileToConvertError{}
+
+	if err.Error() != noFileToConvertErrorMessage {
+		t.Errorf("Error returned a wrong message: got %s want %s", err.Error(), noFileToConvertErrorMessage)
+	}
+}