'Engineer mode test tool' app - What do the codes do? I was curious and installed the Engineer mode test tool app. It listed 'codes' and for most of them it wasn't written what they do. I couldn't resist stupidity and entered a few of them.

After entering one of the codes (listed under Google Service Framework in the app) my phone rebooted and the Android icon was shown and it said "erasing". I had a mini heart attack because I thought I had reset my phone. A white screen showed up saying something like "Enter password to unlock device". It said I have 30 attempts so I tried entering every password that I could remember but nothing worked. The counter said that I used just one guess no matter how many passwords I entered.

In the end I had to factory reset my phone because I needed it, but my data was on the SD card; as it was adopted I lost all my data.

What have I done by entering that code?

What was that screen that I saw?
This looks like a case for Sherlock Holmes.

You can try reinstalling the app, and checking / trying a few things that will help you remember what you did and what you got (the object of your question), in what you would consider a harmless way.

The follwoing lists of codes may also help you remembering; there are many other lists around. Keep in mind that some of the codes are exclusive to specific manufacturers and may not work on all brands/models/carriers.
Showing details on your case in the OP might help.
Comparing with the codes listed under Google Service Framework in the app would help narrowing down the hunting.


110 Android Secret Codes, Hidden Menu, and Dialler Codes.
Secret Codes : Use at your own risk.
Hidden Android Secret Codes &amp; Their Usage.
Android Hidden Codes.


Once you know the code you entered, it is likely trivial to answer your questions:


  What have I done by entering that code?
  
  What was that screen that I saw?