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/attachment_test.go

@@ -0,0 +1,64 @@
+package app
+
+import (
+	"bytes"
+	"io"
+	"net/http"
+	"testing"
+
+	"github.com/xanzy/go-gitlab"
+)
+
+type fakeFileUploaderClient struct {
+	testBase
+}
+
+func (f fakeFileUploaderClient) UploadFile(pid interface{}, content io.Reader, filename string, options ...gitlab.RequestOptionFunc) (*gitlab.ProjectFile, *gitlab.Response, error) {
+	resp, err := f.handleGitlabError()
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return &gitlab.ProjectFile{}, resp, nil
+}
+
+type fakeFileReader struct{}
+
+func (f fakeFileReader) ReadFile(path string) (io.Reader, error) {
+	return &bytes.Reader{}, nil
+}
+
+func TestAttachmentHandler(t *testing.T) {
+	attachmentTestRequestData := AttachmentRequest{
+		FileName: "some_file_name",
+		FilePath: "some_file_path",
+	}
+
+	t.Run("Returns 200-status response after upload", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/attachment", attachmentTestRequestData)
+		svc := attachmentService{testProjectData, fakeFileReader{}, fakeFileUploaderClient{}}
+		data := getSuccessData(t, svc, request)
+		assert(t, data.Status, http.StatusOK)
+		assert(t, data.Message, "File uploaded successfully")
+	})
+
+	t.Run("Disallows non-POST method", func(t *testing.T) {
+		request := makeRequest(t, http.MethodGet, "/attachment", nil)
+		svc := attachmentService{testProjectData, fakeFileReader{}, fakeFileUploaderClient{}}
+		data := getFailData(t, svc, request)
+		checkBadMethod(t, data, http.MethodPost)
+	})
+	t.Run("Handles errors from Gitlab client", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/attachment", attachmentTestRequestData)
+		svc := attachmentService{testProjectData, fakeFileReader{}, fakeFileUploaderClient{testBase{errFromGitlab: true}}}
+		data := getFailData(t, svc, request)
+		checkErrorFromGitlab(t, data, "Could not upload some_file_name to Gitlab")
+	})
+
+	t.Run("Handles non-200s from Gitlab client", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/attachment", attachmentTestRequestData)
+		svc := attachmentService{testProjectData, fakeFileReader{}, fakeFileUploaderClient{testBase{status: http.StatusSeeOther}}}
+		data := getFailData(t, svc, request)
+		checkNon200(t, data, "Could not upload some_file_name to Gitlab", "/attachment")
+	})
+}