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/nullreader/nullreader.go

@@ -0,0 +1,10 @@
+package nullreader
+
+// NullReader is a struct that implements the io.Reader interface and returns nothing when reading
+// from it.
+type NullReader struct{}
+
+func (r NullReader) Read(_ []byte) (int, error) {
+	// An empty select blocks forever.
+	select {}
+}

pkg/nullreader/nullreader_test.go

@@ -0,0 +1,20 @@
+package nullreader
+
+import (
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gitlab.hpi.de/codeocean/codemoon/poseidon/tests"
+	"testing"
+)
+
+func TestNullReaderDoesNotReturnImmediately(t *testing.T) {
+	reader := &NullReader{}
+	readerReturned := make(chan bool)
+	go func() {
+		p := make([]byte, 0, 5)
+		_, err := reader.Read(p)
+		require.NoError(t, err)
+		close(readerReturned)
+	}()
+	assert.False(t, tests.ChannelReceivesSomething(readerReturned, tests.ShortTimeout))
+}