#155 refactor and synchronise writing to CodeOcean. (#174)

* #155 refactor and synchronise writing to CodeOcean.

* Reduce complexity of input parsing.

* Update typo in internal/api/ws/codeocean_writer.go

Co-authored-by: Sebastian Serth <MrSerth@users.noreply.github.com>

internal/api/ws/connection.go

@@ -0,0 +1,14 @@
+package ws
+
+import (
+	"io"
+)
+
+// Connection is an internal interface for websocket.Conn in order to mock it for unit tests.
+type Connection interface {
+	WriteMessage(messageType int, data []byte) error
+	Close() error
+	NextReader() (messageType int, r io.Reader, err error)
+	CloseHandler() func(code int, text string) error
+	SetCloseHandler(handler func(code int, text string) error)
+}