bpo-35798: Add test.support.check_syntax_warning(). (#11895)

It checks that a SyntaxWarning is raised when compile specified
statement, that it is raised only once, that it is converted to
a SyntaxError when raised as exception, and that both warning and
exception objects have corresponding attributes.

1 files changed, 29 insertions, 0 deletions

diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index 436f648..9b75a21 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -86,6 +86,7 @@ __all__ = [
     # unittest
     "is_resource_enabled", "requires", "requires_freebsd_version",
     "requires_linux_version", "requires_mac_ver", "check_syntax_error",
+    "check_syntax_warning",
     "TransientResource", "time_out", "socket_peer_reset", "ioerror_peer_reset",
     "transient_internet", "BasicTestRunner", "run_unittest", "run_doctest",
     "skip_unless_symlink", "requires_gzip", "requires_bz2", "requires_lzma",
@@ -1113,6 +1114,7 @@ def make_bad_fd():
         file.close()
         unlink(TESTFN)
 
+
 def check_syntax_error(testcase, statement, errtext='', *, lineno=None, offset=None):
     with testcase.assertRaisesRegex(SyntaxError, errtext) as cm:
         compile(statement, '<test string>', 'exec')
@@ -1124,6 +1126,33 @@ def check_syntax_error(testcase, statement, errtext='', *, lineno=None, offset=N
     if offset is not None:
         testcase.assertEqual(err.offset, offset)
 
+def check_syntax_warning(testcase, statement, errtext='', *, lineno=1, offset=None):
+    # Test also that a warning is emitted only once.
+    with warnings.catch_warnings(record=True) as warns:
+        warnings.simplefilter('always', SyntaxWarning)
+        compile(statement, '<testcase>', 'exec')
+    testcase.assertEqual(len(warns), 1, warns)
+
+    warn, = warns
+    testcase.assertTrue(issubclass(warn.category, SyntaxWarning), warn.category)
+    if errtext:
+        testcase.assertRegex(str(warn.message), errtext)
+    testcase.assertEqual(warn.filename, '<testcase>')
+    testcase.assertIsNotNone(warn.lineno)
+    if lineno is not None:
+        testcase.assertEqual(warn.lineno, lineno)
+
+    # SyntaxWarning should be converted to SyntaxError when raised,
+    # since the latter contains more information and provides better
+    # error report.
+    with warnings.catch_warnings(record=True) as warns:
+        warnings.simplefilter('error', SyntaxWarning)
+        check_syntax_error(testcase, statement, errtext,
+                           lineno=lineno, offset=offset)
+    # No warnings are leaked when a SyntaxError is raised.
+    testcase.assertEqual(warns, [])
+
+
 def open_urlresource(url, *args, **kw):
     import urllib.request, urllib.parse