From 7d66e4eae1cc5989df07e140f2ff6949416c2c18 Mon Sep 17 00:00:00 2001
From: Bruno Oliveira <nicoddemus@gmail.com>
Date: Mon, 3 Oct 2016 20:47:44 -0300
Subject: [PATCH] Display full traceback from Import errors when collecting
 test modules

Fix #1976
---
 CHANGELOG.rst              |  9 ++++++++-
 _pytest/python.py          | 13 ++++++++-----
 testing/acceptance_test.py |  2 +-
 testing/python/collect.py  | 22 +++++++++++++++++++++-
 testing/test_collection.py | 11 -----------
 testing/test_terminal.py   |  2 +-
 6 files changed, 39 insertions(+), 20 deletions(-)

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 6abd5006a..96a257781 100644
--- a/CHANGELOG.rst
+++ b/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
 =====
 
diff --git a/_pytest/python.py b/_pytest/python.py
index 548d7cfa5..74bb4de43 100644
--- a/_pytest/python.py
+++ b/_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"
-                "Original error message:\n'%s'\n"
-                "Make sure your test modules/packages have valid Python names."
-                % (self.fspath, exc or exc_class)
+                "ImportError while importing test module '{fspath}'.\n"
+                "Hint: make sure your test modules/packages have valid Python names.\n"
+                "Original traceback:\n"
+                "{traceback}".format(fspath=self.fspath, traceback=formatted_tb)
             )
         except _pytest.runner.Skipped as e:
             if e.allow_module_level:
diff --git a/testing/acceptance_test.py b/testing/acceptance_test.py
index b03f7fe4c..88e3fa449 100644
--- a/testing/acceptance_test.py
+++ b/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
 
diff --git a/testing/python/collect.py b/testing/python/collect.py
index 843f26a73..04ce53a54 100644
--- a/testing/python/collect.py
+++ b/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):
diff --git a/testing/test_collection.py b/testing/test_collection.py
index 8e44ba55d..71a64c3c9 100644
--- a/testing/test_collection.py
+++ b/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("""
diff --git a/testing/test_terminal.py b/testing/test_terminal.py
index fc6f3b7b1..66214c80e 100644
--- a/testing/test_terminal.py
+++ b/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*",
         ])