Display full traceback from Import errors when collecting test modules

Fix #1976

CHANGELOG.rst

@@ -3,13 +3,20 @@
 
 *
 
-*
+* Import errors when collecting test modules now display the full traceback (`#1976`_).
+  Thanks `@cwitty`_ for the report and `@nicoddemus`_ for the PR.
 
 *
 
 *
 
 
+.. _@cwitty: https://github.com/cwitty
+
+.. _#1976: https://github.com/pytest-dev/pytest/issues/1976
+
+
+
 3.0.3
 =====
 

_pytest/python.py

@@ -424,12 +424,15 @@ class Module(pytest.File, PyCollector):
                  % e.args
             )
         except ImportError:
-            exc_class, exc, _ = sys.exc_info()
+            import traceback
+            stream = py.io.TextIO()
+            traceback.print_exc(file=stream)
+            formatted_tb = stream.getvalue()
             raise self.CollectError(
-                "ImportError while importing test module '%s'.\n"
+                "ImportError while importing test module '{fspath}'.\n"
-                "Original error message:\n'%s'\n"
+                "Hint: make sure your test modules/packages have valid Python names.\n"
-                "Make sure your test modules/packages have valid Python names."
+                "Original traceback:\n"
-                % (self.fspath, exc or exc_class)
+                "{traceback}".format(fspath=self.fspath, traceback=formatted_tb)
             )
         except _pytest.runner.Skipped as e:
             if e.allow_module_level:

testing/acceptance_test.py

@@ -120,7 +120,7 @@ class TestGeneralUsage:
         result.stdout.fnmatch_lines([
             #XXX on jython this fails:  ">   import import_fails",
             "ImportError while importing test module*",
-            "'No module named *does_not_work*",
+            "*No module named *does_not_work*",
         ])
         assert result.ret == 2
 

testing/python/collect.py

@@ -68,9 +68,29 @@ class TestModule:
         result = testdir.runpytest("-rw")
         result.stdout.fnmatch_lines([
             "ImportError while importing test module*test_one.part1*",
-            "Make sure your test modules/packages have valid Python names.",
+            "Hint: make sure your test modules/packages have valid Python names.",
         ])
 
+    def test_show_full_traceback_import_error(self, testdir):
+        """Import errors when collecting modules should display the full traceback (#1976)."""
+        testdir.makepyfile(
+            foo_traceback_import_error="""
+               from bar_traceback_import_error import NOT_AVAILABLE
+           """,
+            bar_traceback_import_error="",
+        )
+        testdir.makepyfile("""
+               import foo_traceback_import_error
+        """)
+        result = testdir.runpytest()
+        result.stdout.fnmatch_lines([
+            "ImportError while importing test module*",
+            "Original traceback:",
+            "*from bar_traceback_import_error import NOT_AVAILABLE",
+            "*cannot import name *NOT_AVAILABLE*",
+        ])
+        assert result.ret == 2
+
 
 class TestClass:
     def test_class_with_init_warning(self, testdir):

testing/test_collection.py

@@ -172,17 +172,6 @@ class TestCollectPluginHookRelay:
         assert "world" in wascalled
 
 class TestPrunetraceback:
-    def test_collection_error(self, testdir):
-        p = testdir.makepyfile("""
-            import not_exists
-        """)
-        result = testdir.runpytest(p)
-        assert "__import__" not in result.stdout.str(), "too long traceback"
-        result.stdout.fnmatch_lines([
-            "*ERROR collecting*",
-            "ImportError while importing test module*",
-            "'No module named *not_exists*",
-        ])
 
     def test_custom_repr_failure(self, testdir):
         p = testdir.makepyfile("""

testing/test_terminal.py

@@ -667,7 +667,7 @@ class TestGenericReporting:
         result = testdir.runpytest(*option.args)
         result.stdout.fnmatch_lines([
             "ImportError while importing*",
-            "'No module named *xyz*",
+            "*No module named *xyz*",
             "*1 error*",
         ])