Add test for bad configuration

config/config.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"errors"
 	"github.com/TwinProduction/gatus/core"
 	"gopkg.in/yaml.v2"
 	"io/ioutil"
@@ -11,7 +12,10 @@ type Config struct {
 	Services []*core.Service `yaml:"services"`
 }
 
-var config *Config
+var (
+	ErrNoServiceInConfig = errors.New("configuration file should contain at least 1 service")
+	config               *Config
+)
 
 func Get() *Config {
 	if config == nil {
@@ -24,23 +28,26 @@ func Get() *Config {
 	return config
 }
 
-func readConfigurationFile(fileName string) (*Config, error) {
-	if bytes, err := ioutil.ReadFile(fileName); err == nil {
+func readConfigurationFile(fileName string) (config *Config, err error) {
+	var bytes []byte
+	if bytes, err = ioutil.ReadFile(fileName); err == nil {
 		// file exists, so we'll parse it and return it
-		return parseConfigBytes(bytes)
-	} else {
-		return nil, err
+		return parseAndValidateConfigBytes(bytes)
 	}
+	return
 }
 
-func parseConfigBytes(yamlBytes []byte) (config *Config, err error) {
+func parseAndValidateConfigBytes(yamlBytes []byte) (config *Config, err error) {
 	err = yaml.Unmarshal(yamlBytes, &config)
-	if err != nil {
-		return
-	}
-	for _, service := range config.Services {
-		if service.Interval == 0 {
-			service.Interval = 10 * time.Second
+	// Check if the configuration file at least has services.
+	if config == nil || len(config.Services) == 0 {
+		err = ErrNoServiceInConfig
+	} else {
+		// Set the default values if they aren't set
+		for _, service := range config.Services {
+			if service.Interval == 0 {
+				service.Interval = 10 * time.Second
+			}
 		}
 	}
 	return