Monkeypatch test to check that GMTCLibNotFoundError is raised properly

pygmt/clib/loading.py

@@ -77,7 +77,7 @@ def clib_names(os_name):
     elif os_name.startswith("freebsd"):  # FreeBSD
         libnames = ["libgmt.so"]
     else:
-        raise GMTOSError(f'Operating system "{sys.platform}" not supported.')
+        raise GMTOSError(f'Operating system "{os_name}" not supported.')
     return libnames
 
 
@@ -114,8 +114,9 @@ def clib_full_names(env=None):
         lib_fullpath = sp.check_output(
             ["gmt", "--show-library"], encoding="utf-8"
         ).rstrip("\n")
+        assert os.path.exists(lib_fullpath)
         yield lib_fullpath
-    except FileNotFoundError:  # command not found
+    except (FileNotFoundError, AssertionError):  # command not found
         pass
 
     # Search for DLLs in PATH (done by calling "find_library")

pygmt/tests/test_clib_loading.py

@@ -1,6 +1,9 @@
 """
 Test the functions that load libgmt
 """
+import subprocess
+import sys
+
 import pytest
 from pygmt.clib.loading import check_libgmt, clib_names, load_libgmt
 from pygmt.exceptions import GMTCLibError, GMTCLibNotFoundError, GMTOSError
@@ -17,6 +20,21 @@ def test_load_libgmt():
     check_libgmt(load_libgmt())
 
 
+@pytest.mark.skipif(sys.platform == "win32", reason="run on UNIX platforms only")
+def test_load_libgmt_fails(monkeypatch):
+    """
+    Test that GMTCLibNotFoundError is raised when GMT's shared library cannot
+    be found.
+    """
+    with monkeypatch.context() as mpatch:
+        mpatch.setattr(sys, "platform", "win32")  # pretend to be on Windows
+        mpatch.setattr(
+            subprocess, "check_output", lambda cmd, encoding: "libfakegmt.so"
+        )
+        with pytest.raises(GMTCLibNotFoundError):
+            check_libgmt(load_libgmt())
+
+
 def test_load_libgmt_with_a_bad_library_path(monkeypatch):
     "Test that loading still works when given a bad library path."
     # Set a fake "GMT_LIBRARY_PATH"