From these definitions and my own sense, test out implies practical testing along the lines of trying out, exploring, or putting something to the test. Testing out may also imply something less formal or rigorous than testing. You might test cameras for a magazine review (with your qualitative and quantitative results) and cursorily test out models at the store when shopping for one.
To subject to a test of any kind; to try, put to the proof; to
ascertain the existence, genuineness, or quality of. to test out,
to put (a theory, etc.) to a practical test.
To test out the value of radio publicity.
Legal philosophers could back up these efforts by testing out some of their theories with research projects. OED
test out (v.)
(transitive) To try or experiment with (something or someone) in order
to see if it works, is true, or is successful.
You will also have to test out any HTML code or Java applets that you include, and you will have to test the whole site once it is published to a server.
Poland tested England out with their intensity and physical commitment but Southgate's side stood strong while also having to deal with a crowd of 56,212 made up entirely of home support.
explore (something one has little experience with), especially to do
so in a safe environment.
(transitive) To explore how (someone)
responds to something; To feel someone out.
demonstrate a certain result in a test, especially a successful
(intransitive) To pass a placement test that enables one to
avoid taking a course. Wiktionary
To put to test or proof: TRY —often used with out m-w