Restructure project

We previously didn't really had any structure in our project apart
from creating a new folder for each package in our project root.
Now that we have accumulated some packages, we use the well-known
Golang project layout in order to clearly communicate our intent
with packages. See https://github.com/golang-standards/project-layout

pkg/logging/logging_test.go

@@ -0,0 +1,48 @@
+package logging
+
+import (
+	"github.com/sirupsen/logrus"
+	"github.com/sirupsen/logrus/hooks/test"
+	"github.com/stretchr/testify/assert"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func mockHTTPStatusHandler(status int) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(status)
+	})
+}
+
+func TestHTTPMiddlewareWarnsWhenInternalServerError(t *testing.T) {
+	var hook *test.Hook
+	log, hook = test.NewNullLogger()
+	InitializeLogging(logrus.DebugLevel.String())
+
+	request, err := http.NewRequest(http.MethodGet, "/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	recorder := httptest.NewRecorder()
+	HTTPLoggingMiddleware(mockHTTPStatusHandler(500)).ServeHTTP(recorder, request)
+
+	assert.Equal(t, 1, len(hook.Entries))
+	assert.Equal(t, logrus.WarnLevel, hook.LastEntry().Level)
+}
+
+func TestHTTPMiddlewareDebugsWhenStatusOK(t *testing.T) {
+	var hook *test.Hook
+	log, hook = test.NewNullLogger()
+	InitializeLogging(logrus.DebugLevel.String())
+
+	request, err := http.NewRequest(http.MethodGet, "/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	recorder := httptest.NewRecorder()
+	HTTPLoggingMiddleware(mockHTTPStatusHandler(200)).ServeHTTP(recorder, request)
+
+	assert.Equal(t, 1, len(hook.Entries))
+	assert.Equal(t, logrus.DebugLevel, hook.LastEntry().Level)
+}