tests the download function in _utils.py

tests/unit_tests/test_utils.py

@@ -0,0 +1,26 @@
+import os
+import filecmp
+
+from openmc import _utils
+import pytest
+
+@pytest.fixture()
+def download_photos(run_in_tmpdir):
+    """use _utils download() function to download the same picture three times,
+       twice to get unique names, & a third time to use the already downloaded
+       block of code"""
+    _utils.download("https://i.ibb.co/HhKFc8x/small.jpg")
+    _utils.download("https://tinyurl.com/y4t38ugb")
+    _utils.download("https://tinyurl.com/y4t38ugb", as_browser=True)
+
+
+def test_checksum_error(run_in_tmpdir):
+    """use download() in such a way that will test the checksum error line"""
+    phrase = "MD5 checksum for y4t38ugb"
+    with pytest.raises(OSError, match=phrase):
+        _utils.download("https://tinyurl.com/y4t38ugb", as_browser=True,
+                        checksum="not none")
+
+
+def test_photos(download_photos):
+    assert filecmp.cmp("small.jpg", "y4t38ugb")