Fix context output handling for doctests

Show full context of doctest source in the pytest output, if the lineno of
failed example in the docstring is < 9.

Author: twmr

_pytest/doctest.py

@@ -120,7 +120,7 @@ def repr_failure(self, excinfo):
                 lines = ["%03d %s" % (i + test.lineno + 1, x)
                          for (i, x) in enumerate(lines)]
                 # trim docstring error lines to 10
-                lines = lines[example.lineno - 9:example.lineno + 1]
+                lines = lines[max(example.lineno - 9, 0):example.lineno + 1]
             else:
                 lines = ['EXAMPLE LOCATION UNKNOWN, not showing all tests of that example']
                 indent = '>>>'

changelog/2882.bugfix

@@ -0,0 +1 @@
+Show full context of doctest source in the pytest output, if the lineno of failed example in the docstring is < 9.

testing/test_doctest.py

@@ -173,7 +173,7 @@ def test_doctest_unexpected_exception(self, testdir):
             "*UNEXPECTED*ZeroDivision*",
         ])
 
-    def test_docstring_context_around_error(self, testdir):
+    def test_docstring_partial_context_around_error(self, testdir):
         """Test that we show some context before the actual line of a failing
         doctest.
         """
@@ -213,6 +213,32 @@ def foo():
         assert 'text-line-2' not in result.stdout.str()
         assert 'text-line-after' not in result.stdout.str()
 
+    def test_docstring_full_context_around_error(self, testdir):
+        """Test that we show the whole context before the actual line of a failing
+        doctest, provided that the context is up to 10 lines long.
+        """
+        testdir.makepyfile('''
+            def foo():
+                """
+                text-line-1
+                text-line-2
+
+                >>> 1 + 1
+                3
+                """
+        ''')
+        result = testdir.runpytest('--doctest-modules')
+        result.stdout.fnmatch_lines([
+            '*docstring_context_around_error*',
+            '003*text-line-1',
+            '004*text-line-2',
+            '006*>>> 1 + 1',
+            'Expected:',
+            '    3',
+            'Got:',
+            '    2',
+        ])
+
     def test_doctest_linedata_missing(self, testdir):
         testdir.tmpdir.join('hello.py').write(_pytest._code.Source("""
             class Fun(object):