In 2005 I published an article: ‘An Unidentified Theological Fragment from the Fifth Century in a Private Collection in Cambridge (de Hamel MS 373)’ Tyndale Bulletin 56 (2005), 35-38. This article dealt with the document that is pictured here, offering a transcription, and suggested it was a Christian text dealing with church order, but one which I had been unable to identify (hence the title!).
Recently two scholars who have been working on the Latin texts purchased with this Greek text have argued (I think persuasively) that this fragment represents a piece of the only surviving Greek manuscript of the Testamentum Domini (for some of the back story see here and here).
S. Corcoran, & B. Salway, ‘A Newly Identified Greek Fragment of the Testamentum Domini’ Journal of Theological Studies 62 (2011), 118-135. So kudos to them for solving the mystery - an excellent outcome all round.