update: improve coverage

README.md

@@ -1,6 +1,6 @@
 > Package captcha provides a simple API for captcha generation
 
-<div align="center">
+<div>
 
 [![GoDoc](https://godoc.org/github.com/steambap/captcha?status.svg)](https://godoc.org/github.com/steambap/captcha)
 [![Build Status](https://travis-ci.org/steambap/captcha.svg)](https://travis-ci.org/steambap/captcha)

captcha_test.go

@@ -2,10 +2,12 @@ package captcha
 
 import (
 	"bytes"
+	"image/color"
 	"testing"
 )
 
 func TestNewCaptcha(t *testing.T) {
+	New(36, 12)
 	data, err := New(150, 50)
 	if err != nil {
 		t.Fatal(err)
@@ -13,3 +15,24 @@ func TestNewCaptcha(t *testing.T) {
 	buf := new(bytes.Buffer)
 	data.WriteTo(buf)
 }
+
+func TestNewCaptchaOptions(t *testing.T) {
+	New(100, 34, func(options *Options) {
+		options.BackgroundColor = color.Opaque
+		options.CharPreset = "1234567890"
+		options.CurveNumber = 0
+		options.TextLength = 6
+	})
+}
+
+func TestCovNilFontError(t *testing.T) {
+	temp := ttfFont
+	ttfFont = nil
+
+	_, err := New(150, 50)
+	if err == nil {
+		t.Fatal("Expect to get nil font error")
+	}
+
+	ttfFont = temp
+}