In an effort to be more universally appropriate to the test suite, I …

…moved the headerToModule() to a top level of the Qt.py. This allowed the function itself to be tested and no longer relies on the variety of paths the code may take in the when calling the QtCompat.loadui().

Qt.py

@@ -874,6 +874,23 @@ def get_arg(index):
     return app.translate(*sanitized_args)
 
 
+def _headerToModule(header):
+    """
+    Translate a header file to python module path
+    foo/bar.h => foo.bar
+    """
+
+    # Only manipulate header files, identified by the `.h` ext.
+    if header.endswith(".h") is False:
+        return header
+
+    # Remove header extension
+    module = os.path.splitext(header)[0]
+
+    # Replace os separator by python module separator
+    return module.replace("/", ".").replace("\\", ".")
+
+
 def _loadUi(uifile, baseinstance=None):
     """Dynamically load a user interface from the given `uifile`
 
@@ -925,22 +942,6 @@ def _loadCustomWidgets(self, etree):
                 objects. Then we can directly use them in createWidget method.
                 """
 
-                def headerToModule(header):
-                    """
-                    Translate a header file to python module path
-                    foo/bar.h => foo.bar
-                    """
-
-                    if header.endswith(".h") is False:
-                        # Only manipulate header files, identified by the `.h` ext.
-                        return header
-
-                    # Remove header extension
-                    module = os.path.splitext(header)[0]
-
-                    # Replace os separator by python module separator
-                    return module.replace("/", ".").replace("\\", ".")
-
                 custom_widgets = etree.find("customwidgets")
 
                 if custom_widgets is None:
@@ -949,13 +950,7 @@ def headerToModule(header):
                 for custom_widget in custom_widgets:
                     class_name = custom_widget.find("class").text
                     header = custom_widget.find("header").text
-                    try:
-                        header = headerToModule(header)
-                        module = importlib.import_module(header)
-                    except ImportError as _error:
-                        # ReRaising the ImportError with a more informative
-                        # message to aid in the creation of Tests for this case.
-                        raise ImportError("No module named '%s'" % header)
+                    module = importlib.import_module(_headerToModule(header))
                     self.custom_widgets[class_name] = getattr(module,
                                                               class_name)
 

tests.py

@@ -449,25 +449,10 @@ def test_load_ui_customwidget():
     app.exit()
 
 
-def _rewrite_file(file, current, provided):
-    with open(file, "r") as f:
-        new = f.read().replace(
-            "<header>" + current + "</header>",
-            "<header>" + provided + "</header>"
-        )
-    with open(self.ui_qpycustomwidget, "w") as f:
-        f.write(new)
-
-
-def test_load_ui_pycustomwidget():
-    """Tests to see if loadUi loads a custom widget from different sources,
-    such as a Python path or a .h path can be parsed properly.
-
-    The structure of the current code does not provide direct access to the
-    headertomodule function. Instead, the test updates the temp.ui file to
-    contain a different header and tries to load the UI. All cases are
-    designed to trigger a ModuleImport Exception which reports the path
-    expected.
+def test_headerToModule():
+    """
+    Tests to see if headerToModule manipulates the path passed in appropriately.
+    - It should only affect `Header` files and paths, marked with an .h extension.
     """
 
     path_tests = {
@@ -489,30 +474,13 @@ def test_load_ui_pycustomwidget():
         "path/to/module": "path/to/module",
         "module.py": "module.py",
     }
-    import sys
-    from Qt import QtWidgets, QtCompat
 
-    app = QtWidgets.QApplication(sys.argv)
-    win = QtWidgets.QMainWindow()
+    import Qt
 
-    current = "tests"
     for provided, expected in path_tests.items():
-        _rewrite_file(self.ui_qpycustomwidget, current, provided)
-        current = provided
+        result = Qt._headerToModule(provided)
+        assert result == expected, "Provided: %s expected: %s got: %s" % (provided, expected, result)
 
-        try:
-            # actual test
-            QtCompat.loadUi(self.ui_qpycustomwidget, win)
-
-        except ImportError as error:
-            # Since the loadUi is a blackbox it is not possible to test the
-            # `headertomodule` function directly. Test if the ImportError
-            # error contains the correct import path.
-            result = str(error).split("'")[1]
-            assert result == expected, (
-                    "Provided: %s expected: %s got: %s" % (provided, expected, result)
-            )
-    app.exit()
 
 def test_load_ui_invalidpath():
     """Tests to see if loadUi successfully fails on invalid paths"""