What is a software test engineer?

Outsourced definition

Here's a link of someone else's definition of a software test engineer.

My definition

An overqualified quality assurance analyst, who develops software used to test other software.

The software development life cycle

Here's a link if you want to dive deeper to the SDLC, but I am bringing it up to outline the role of a SET in relation to the SDLC.

Now you may be wondering, I don't see "software engineer in test" anywhere. This is because the team format I showed above, is more of an outdated model; as the complexity of the role of a "quality assurance analyst" has increased recently as the scope of their responsibilities has changed. 

Traditionally quality assurance analysts had the responsibility of manually testing software, they never had to develop any sort of codebase to fulfill their role. With the increase in complexity of applications, manual testing became troublesome to sustain over the long term (though I must stress that manual testing is VERY important and 100% automation is a wrong goal for any company to stride towards). 

The industries answer to the unsustainability; was automated testing. The only issue was, in order to automate testing; testing scripts needed to be developed and these scripts are developed with code. So now there was a problem, industries needed quality assurance analysts who had no experience developing code; to now needing to be able to code. 

The software test engineer

So, as a result; what was born was a new role: the software engineer in test (SET), also known as a quality engineer (QE) or software development engineer in test (SDET). Who has the responsibility to develop software that is used to test other software.