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/create_mr_test.go

@@ -0,0 +1,80 @@
+package app
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/xanzy/go-gitlab"
+)
+
+type fakeMergeCreatorClient struct {
+	testBase
+}
+
+func (f fakeMergeCreatorClient) CreateMergeRequest(pid interface{}, opt *gitlab.CreateMergeRequestOptions, options ...gitlab.RequestOptionFunc) (*gitlab.MergeRequest, *gitlab.Response, error) {
+	resp, err := f.handleGitlabError()
+	if err != nil {
+		return nil, nil, err
+	}
+	return &gitlab.MergeRequest{}, resp, nil
+}
+
+func TestCreateMr(t *testing.T) {
+	var testCreateMrRequestData = CreateMrRequest{
+		Title:        "Some title",
+		Description:  "Some description",
+		TargetBranch: "main",
+		DeleteBranch: false,
+		Squash:       false,
+	}
+	t.Run("Creates an MR", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/create_mr", testCreateMrRequestData)
+		svc := mergeRequestCreatorService{testProjectData, fakeMergeCreatorClient{}}
+		data := getSuccessData(t, svc, request)
+		assert(t, data.Message, "MR 'Some title' created")
+		assert(t, data.Status, http.StatusOK)
+	})
+
+	t.Run("Disallows non-POST methods", func(t *testing.T) {
+		request := makeRequest(t, http.MethodGet, "/create_mr", testCreateMrRequestData)
+		svc := mergeRequestCreatorService{testProjectData, fakeMergeCreatorClient{}}
+		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, "/create_mr", testCreateMrRequestData)
+		svc := mergeRequestCreatorService{testProjectData, fakeMergeCreatorClient{testBase{errFromGitlab: true}}}
+		data := getFailData(t, svc, request)
+		checkErrorFromGitlab(t, data, "Could not create MR")
+	})
+
+	t.Run("Handles non-200s from Gitlab client", func(t *testing.T) {
+		request := makeRequest(t, http.MethodPost, "/create_mr", testCreateMrRequestData)
+		svc := mergeRequestCreatorService{testProjectData, fakeMergeCreatorClient{testBase{status: http.StatusSeeOther}}}
+		data := getFailData(t, svc, request)
+		checkNon200(t, data, "Could not create MR", "/create_mr")
+	})
+
+	t.Run("Handles missing titles", func(t *testing.T) {
+		reqData := testCreateMrRequestData
+		reqData.Title = ""
+		request := makeRequest(t, http.MethodPost, "/create_mr", reqData)
+		svc := mergeRequestCreatorService{testProjectData, fakeMergeCreatorClient{}}
+		data := getFailData(t, svc, request)
+		assert(t, data.Status, http.StatusBadRequest)
+		assert(t, data.Message, "Could not create MR")
+		assert(t, data.Details, "Title cannot be empty")
+	})
+
+	t.Run("Handles missing target branch", func(t *testing.T) {
+		reqData := testCreateMrRequestData
+		reqData.TargetBranch = ""
+		request := makeRequest(t, http.MethodPost, "/create_mr", reqData)
+		svc := mergeRequestCreatorService{testProjectData, fakeMergeCreatorClient{}}
+		data := getFailData(t, svc, request)
+		assert(t, data.Status, http.StatusBadRequest)
+		assert(t, data.Message, "Could not create MR")
+		assert(t, data.Details, "Target branch cannot be empty")
+	})
+}