Fix warning when failed import is parent package

qiskit/utils/lazy_tester.py

@@ -292,9 +292,11 @@ def _is_available(self):
             try:
                 imported = importlib.import_module(module)
             except ModuleNotFoundError as exc:
-                if exc.name == module:
-                    # If the module that wasn't found is the one we were explicitly searching for,
-                    # then it's just not installed.
+                failed_parts = exc.name.split(".")
+                target_parts = module.split(".")
+                if failed_parts == target_parts[: len(failed_parts)]:
+                    # If the module that wasn't found is the one we were explicitly searching for
+                    # (or one of its parents), then it's just not installed.
                     return False
                 # Otherwise, we _did_ find the module, it just didn't import, which is a problem.
                 failed_modules[module] = exc

test/python/utils/test_lazy_loaders.py

@@ -17,6 +17,7 @@
 import importlib.abc
 import importlib.util
 import sys
+import warnings
 from unittest import mock
 
 import ddt
@@ -98,6 +99,23 @@ def test_evaluates_correctly_false(self, test_generator):
         if test_generator():
             self.fail("did not evaluate false")
 
+    def test_submodule_import_detects_false_correctly(self):
+        """Test that a lazy import of a submodule where the parent is not available still generates
+        a silent failure."""
+
+        # The idea here is that the base package is what will fail the import, and the corresponding
+        # `ImportError.name` won't be the same as the full path we were trying to import.  We want
+        # to make sure that the "was it found and failed to import?" handling is correct in this
+        # case.
+        def checker():
+            return LazyImportTester("_qiskit_module_does_not_exist_.submodule")
+
+        # Just in case something else is allowing the warnings, but they should be forbidden by
+        # default.
+        with warnings.catch_warnings(record=True) as log:
+            self.assertFalse(checker())
+        self.assertEqual(log, [])
+
     @ddt.data(available_importer, available_process, unavailable_importer, unavailable_process)
     def test_check_occurs_once(self, test_generator):
         """Check that the test of availability is only performed once."""