Merge #14649: clarify DocTestSuite error when there are no docstrings.

Also adds tests to verify the documented behavior (which is probably a bug, as
indicated in the added comments).

Patch by Chris Jerdonek.

1 files changed, 25 insertions, 0 deletions

diff --git a/Lib/test/test_doctest.py b/Lib/test/test_doctest.py
index 44b9554..8f8c7c7 100644
--- a/Lib/test/test_doctest.py
+++ b/Lib/test/test_doctest.py
@@ -1986,6 +1986,31 @@ def test_DocTestSuite():
          >>> suite.run(unittest.TestResult())
          <unittest.result.TestResult run=9 errors=0 failures=4>
 
+       The module need not contain any doctest examples:
+
+         >>> suite = doctest.DocTestSuite('test.sample_doctest_no_doctests')
+         >>> suite.run(unittest.TestResult())
+         <unittest.result.TestResult run=0 errors=0 failures=0>
+
+       However, if DocTestSuite finds no docstrings, it raises an error:
+
+         >>> try:
+         ...     doctest.DocTestSuite('test.sample_doctest_no_docstrings')
+         ... except ValueError as e:
+         ...     error = e
+
+         >>> print(error.args[1])
+         has no docstrings
+
+       You can prevent this error by passing a DocTestFinder instance with
+       the `exclude_empty` keyword argument set to False:
+
+         >>> finder = doctest.DocTestFinder(exclude_empty=False)
+         >>> suite = doctest.DocTestSuite('test.sample_doctest_no_docstrings',
+         ...                              test_finder=finder)
+         >>> suite.run(unittest.TestResult())
+         <unittest.result.TestResult run=0 errors=0 failures=0>
+
        We can use the current module:
 
          >>> suite = test.sample_doctest.test_suite()