Which tester has an in-depth knowledge of the network and systems being tested, including network diagrams, ip addresses, and even the source code of custom applications?

this tester is the white box testing.

Explanation:

Black box testing is the Software testing method which is used to test the software without knowing the internal structure of code or program. White box testing is the software testing method in which internal structure is being known to tester who is going to test the software.

which functions return a valid value without any arguments?

(-blank- and -blank- return a valid value without any arguments.)

1st -blank-

today

sqrt

count

2nd -blank-

round

now

sqrt