Docs: correction to test readme compile instructions

[JBaczuk]

I'm pretty sure this wording is just switched, but correct me if I'm wrong. If you have only changed a test file, you can just build the files in the test folder, no need to build the entire source.

[maflcko]

Our compile tooling will notice that only test files have been modified and thus make will only compile the test files if they have been modified, so the wording as in master sounds correct to me.

[JBaczuk]

I'm just confused because it says, "If you modify a non-test file, use make -C src/test to recompile only what's needed to run the bitcoind tests."

Wouldn't that only compile test files?

[sipa]

@JBaczuk And all core files needed to run those tests. Make reasons about dependencies.

But it won't bother building the bitcoind binary, which isn't needed for the unit tests.

[JBaczuk]

@sipa Ah, ok, sounds like I'm mistaken, then, thanks.