Employment contracts can be oral or written, or oral and written or oral, written and implied.
“The terms of a contract which is partly in writing and partly oral are to be ascertained from a consideration of the whole of the circumstances in which the agreement was struck. As was said by Lockhart J in Finucane v New South Wales Egg Corporation at 520.45 – 521.10: (1988) 80 ALR 486 at 520.45 – 521.10.”
“The contract between the Corporation and Finucane was partly oral, partly in writing and partly by conduct, and in the circumstances the court “is entitled to look at and should look at all the evidence from start to finish in order to see what the bargain was that was struck between the parties” J Evans & Son (Portsmouth) Ltd v Andrea Merzario Ltd  1 WLR 1078 at 1083 per Roskill LJ. The court may have regard to the intentions of the parties by drawing inferences from their words and their conduct in the making of the agreement, having regard also to the subject matter of the agreement and the surrounding circumstances: Allen v Carbone (1975) 132 CLR 528 at 531-2 per Stephen, Mason, Murphy JJ. The court will be prepared to place greater weight on the surrounding circumstances where the statements and actions of the parties have not been merged in a formal document exhaustively setting out. the terms of the bargain: Codelfa Construction Pty Ltd v State Rail Authority of New South Wales (1982) 149 CLR 337 at 352; 41 ALR 367 at 374-5 per Mason J.”
And see MCPARLAND v ORIGIN OZ HOLDINGS & ORS  FCCA 1534 delivered 5 June 2019 per Egan J