Description of the problem

In our tests, we usually save the output to a GMTTempFile object and then check if the output temporary file exists using the os.path.exists function.

Here is an example test for grd2xyz:

The problem is, GMTTempFile always creates the 0-byte temporary file when GMTTempFile is called, so the temporary file always exists. It means that we can't use os.path.exists to check if functions like grd2xyz write output to a file or not.

Here is a minimal script to verify it:

import os
from pygmt.helpers import GMTTempFile
with GMTTempFile(suffix="txt") as fp:
    print(fp.name, os.path.exists(fp.name), os.path.getsize(fp.name))

the output is: /tmp/pygmt-mhtfhdmltxt True 0.

Possible solutions:

• Improve the GMTTempFile class to make sure that the 0-byte temporary file is not created by GMTTempFile
• Use os.path.getsize to check if the file size is non-zero, rather than using os.path.exists