Better error messages and tests for them

cosmosis/runtime/module.py

@@ -281,25 +281,23 @@ def load_library(filepath):
 
         """
 
-        if filepath.endswith('so') or filepath.endswith('dylib'):
+        if not os.path.exists(filepath):
+            raise SetupError(f"You specified a path {filepath} for a module. "
+                             "This file does not exist.")
+
+        elif filepath.endswith('so') or filepath.endswith('dylib'):
             language = MODULE_LANG_DYLIB
             try:
                 library = ctypes.cdll.LoadLibrary(filepath)
             except OSError as error:
-                exists = os.path.exists(filepath)
-                if exists:
-                    raise SetupError("You specified a path %s for a module. "
-                                     "File exists, but could not be opened. "
-                                     "Error was %s" % (filepath, error))
-                else:
-                    raise SetupError("You specified a path %s for a module. "
-                                     "File does not exist.  Error was %s" %
-                                     (filepath, error))
+                raise SetupError(f"You specified a path {filepath} for a module. "
+                                 f"File exists, but could not be opened. "
+                                 f"Error was {error}")
         elif filepath.endswith(".jl"):
             from . import julia_modules
             library = julia_modules.JuliaModule(filepath)
             language = MODULE_LANG_JULIA
-        else:
+        elif filepath.endswith(".py"):
             language = MODULE_LANG_PYTHON
             dirname, filename = os.path.split(filepath)
             # allows .pyc and .py modules to be used
@@ -313,6 +311,12 @@ def load_library(filepath):
                                  "was unable to load it.  Error was %s" %
                                  (filepath, error))
             sys.path.pop(0)
+        else:
+            raise SetupError(f"You specified a path {filepath} for a module. "
+                             "I do not know what kind of module this is "
+                             "because the suffix is not .so, .dylib, .jl, or .py"
+                             )
+
 
         return library, language
 

cosmosis/test/test_modules.py

@@ -0,0 +1,17 @@
+import cosmosis
+import pytest
+import tempfile
+
+def test_missing_module():
+    with pytest.raises(cosmosis.runtime.SetupError) as error_info:
+        m = cosmosis.Module("pretend", "./this_file_does_not_exist.py")
+
+    assert "file does not exist" in str(error_info.value)
+
+
+def test_wrong_path_type():
+    with tempfile.NamedTemporaryFile(suffix=".x") as f:
+        with pytest.raises(cosmosis.runtime.SetupError) as error_info:
+            m = cosmosis.Module("pretend", f.name)
+
+    assert "do not know what kind of module this is" in str(error_info.value)