Generalize loadConfig method to avoid reading from disk (#5819)

As we move to multiple config backends like local disk and etcd,
config file should not be read from the disk, instead the quick
package should load and verify for duplicate entries.

pkg/quick/quick_test.go

@@ -27,6 +27,8 @@ import (
 	"runtime"
 	"strings"
 	"testing"
+
+	"github.com/tidwall/gjson"
 )
 
 func TestReadVersion(t *testing.T) {
@@ -504,3 +506,31 @@ func TestDeepDiff(t *testing.T) {
 	//		fmt.Printf("DeepDiff[%d]: %s=%v\n", i, field.Name(), field.Value())
 	//	}
 }
+
+func TestCheckDupJSONKeys(t *testing.T) {
+	testCases := []struct {
+		json       string
+		shouldPass bool
+	}{
+		{`{}`, true},
+		{`{"version" : "13"}`, true},
+		{`{"version" : "13", "version": "14"}`, false},
+		{`{"version" : "13", "credential": {"accessKey": "12345"}}`, true},
+		{`{"version" : "13", "credential": {"accessKey": "12345", "accessKey":"12345"}}`, false},
+		{`{"version" : "13", "notify": {"amqp": {"1"}, "webhook":{"3"}}}`, true},
+		{`{"version" : "13", "notify": {"amqp": {"1"}, "amqp":{"3"}}}`, false},
+		{`{"version" : "13", "notify": {"amqp": {"1":{}, "2":{}}}}`, true},
+		{`{"version" : "13", "notify": {"amqp": {"1":{}, "1":{}}}}`, false},
+	}
+
+	for i, testCase := range testCases {
+		err := doCheckDupJSONKeys(gjson.Result{}, gjson.Parse(testCase.json))
+		if testCase.shouldPass && err != nil {
+			t.Errorf("Test %d, should pass but it failed with err = %v", i+1, err)
+		}
+		if !testCase.shouldPass && err == nil {
+			t.Errorf("Test %d, should fail but it succeed.", i+1)
+		}
+	}
+
+}