Fix MR Selection, Go Code Refactor (#358)

refactor: Refactors the Go codebase into a more modular and idiomatic approach
fix: require selection of specific MR when there are multiple targets for a given source branch
feat: Allows for the passing of Gitlab's filter options when choosing an MR, improves MR selection
feat: API to choose an MR from a list based on the provided username's involvement as an assignee/reviewer/author

This is a #MINOR release

cmd/app/reply_test.go

@@ -0,0 +1,45 @@
+package app
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/xanzy/go-gitlab"
+)
+
+type fakeReplyManager struct {
+	testBase
+}
+
+func (f fakeReplyManager) AddMergeRequestDiscussionNote(interface{}, int, string, *gitlab.AddMergeRequestDiscussionNoteOptions, ...gitlab.RequestOptionFunc) (*gitlab.Note, *gitlab.Response, error) {
+	resp, err := f.handleGitlabError()
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return &gitlab.Note{}, resp, err
+}
+
+func TestReplyHandler(t *testing.T) {
+	var testReplyRequest = ReplyRequest{DiscussionId: "abc123", Reply: "Some Reply", IsDraft: false}
+	t.Run("Sends a reply", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/mr/reply", testReplyRequest)
+		svc := replyService{testProjectData, fakeReplyManager{}}
+		data := getSuccessData(t, svc, request)
+		assert(t, data.Message, "Replied to comment")
+		assert(t, data.Status, http.StatusOK)
+	})
+	t.Run("Handles errors from Gitlab client", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/mr/reply", testReplyRequest)
+		svc := replyService{testProjectData, fakeReplyManager{testBase{errFromGitlab: true}}}
+		data := getFailData(t, svc, request)
+		checkErrorFromGitlab(t, data, "Could not leave reply")
+	})
+
+	t.Run("Handles non-200s from Gitlab client", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/mr/reply", testReplyRequest)
+		svc := replyService{testProjectData, fakeReplyManager{testBase{status: http.StatusSeeOther}}}
+		data := getFailData(t, svc, request)
+		checkNon200(t, data, "Could not leave reply", "/mr/reply")
+	})
+}