Fix test suite failure without numpy and improve module init diagnostics

Fixes #357.

tests/conftest.py

@@ -202,3 +202,27 @@ def pytest_namespace():
         'requires_eigen_and_scipy': skipif(not have_eigen or not scipy,
                                            reason="eigen and/or scipy are not installed"),
     }
+
+
+def _test_import_pybind11():
+    """Early diagnostic for test module initialization errors
+
+    When there is an error during initialization, the first import will report the
+    real error while all subsequent imports will report nonsense. This import test
+    is done early (in the pytest configuration file, before any tests) in order to
+    avoid the noise of having all tests fail with identical error messages.
+
+    Any possible exception is caught here and reported manually *without* the stack
+    trace. This further reduces noise since the trace would only show pytest internals
+    which are not useful for debugging pybind11 module issues.
+    """
+    # noinspection PyBroadException
+    try:
+        import pybind11_tests
+    except Exception as e:
+        print("Failed to import pybind11_tests from pytest:")
+        print("  {}: {}".format(type(e).__name__, e))
+        sys.exit(1)
+
+
+_test_import_pybind11()