Don't really plot images in unit tests (#548)

* Don't really plot images in unit tests

* Oops,

Author: delucchi-cmu

pyproject.toml

@@ -81,3 +81,4 @@ target-version = ["py310"]
 [tool.isort]
 profile = "black"
 line_length = 110
+skip_glob = ["benchmarks/env/*"]

tests/hats/inspection/test_visualize_catalog.py

@@ -1,6 +1,7 @@
 from unittest.mock import MagicMock
 
 import astropy.units as u
+import matplotlib as mpl
 import matplotlib.pyplot as plt
 import numpy as np
 import pytest
@@ -30,6 +31,7 @@
 
 # pylint: disable=no-member
 
+mpl.use("Agg")
 
 DEFAULT_CMAP_NAME = "viridis"
 DEFAULT_FOV = (320 * u.deg, 160 * u.deg)