Add gitlab system hook parsing

If you use gitlab system hooks you can now send push/tag_push/merge_request events

gitlab/gitlab_test.go

@@ -2,15 +2,13 @@ package gitlab
 
 import (
 	"bytes"
+	"io"
 	"log"
 	"net/http"
 	"net/http/httptest"
 	"os"
-	"testing"
-
-	"io"
-
 	"reflect"
+	"testing"
 
 	"github.com/stretchr/testify/require"
 )
@@ -266,3 +264,62 @@ func TestWebhooks(t *testing.T) {
 		})
 	}
 }
+
+func TestSystemHooks(t *testing.T) {
+	assert := require.New(t)
+	tests := []struct {
+		name     string
+		event    Event
+		typ      interface{}
+		filename string
+	}{
+		{
+			name:     "PushEvent",
+			event:    PushEvents,
+			typ:      PushEventPayload{},
+			filename: "../testdata/gitlab/push-event.json",
+		},
+		{
+			name:     "TagEvent",
+			event:    TagEvents,
+			typ:      TagEventPayload{},
+			filename: "../testdata/gitlab/tag-event.json",
+		},
+		{
+			name:     "MergeRequestEvent",
+			event:    MergeRequestEvents,
+			typ:      MergeRequestEventPayload{},
+			filename: "../testdata/gitlab/merge-request-event.json",
+		},
+	}
+	for _, tt := range tests {
+		tc := tt
+		client := &http.Client{}
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			payload, err := os.Open(tc.filename)
+			assert.NoError(err)
+			defer func() {
+				_ = payload.Close()
+			}()
+
+			var parseError error
+			var results interface{}
+			server := newServer(func(w http.ResponseWriter, r *http.Request) {
+				results, parseError = hook.Parse(r, tc.event)
+			})
+			defer server.Close()
+			req, err := http.NewRequest(http.MethodPost, server.URL+path, payload)
+			assert.NoError(err)
+			req.Header.Set("Content-Type", "application/json")
+			req.Header.Set("X-Gitlab-Token", "sampleToken!")
+			req.Header.Set("X-Gitlab-Event", "System Hook")
+
+			resp, err := client.Do(req)
+			assert.NoError(err)
+			assert.Equal(http.StatusOK, resp.StatusCode)
+			assert.NoError(parseError)
+			assert.Equal(reflect.TypeOf(tc.typ), reflect.TypeOf(results))
+		})
+	}
+}