Add some test helper functions to create (source) files from tests.

To be used in https://github.com/cython/cython/pull/4241

Cython/TestUtils.py

@@ -5,6 +5,7 @@ import unittest
 import shlex
 import sys
 import tempfile
+import textwrap
 from io import open
 
 from .Compiler import Errors
@@ -225,3 +226,31 @@ def unpack_source_tree(tree_file, workdir, cython_root):
             if cur_file is not None:
                 cur_file.close()
     return workdir, header
+
+
+def write_file(file_path, content, dedent=False):
+    """
+    Write some content (text or bytes) to the file at "file_path".
+    """
+    mode = 'wb' if isinstance(content, bytes) else 'w'
+    if dedent:
+        content = textwrap.dedent(content)
+
+    with open(file_path, mode=mode) as f:
+        f.write(content)
+
+
+def write_newer_file(file_path, newer_than, content, dedent=False):
+    """
+    Write 'content' to the file 'file_path' and make sure it is newer than the file 'newer_than'.
+    """
+    write_file(file_path, content, dedent=dedent)
+
+    try:
+        other_time = os.path.getmtime(newer_than)
+    except OSError:
+        # Support
+        other_time = None
+
+    while other_time is None or other_time >= os.path.getmtime(file_path):
+        write_file(file_path, content, dedent=dedent)

Cython/Tests/TestTestUtils.py

+import os.path
+import unittest
+import tempfile
+import shutil
+
+from ..TestUtils import write_file, write_newer_file
+
+
+class TestTestUtils(unittest.TestCase):
+    def setUp(self):
+        self.temp_dir = tempfile.mkdtemp()
+        self._test_path = lambda filename: os.path.join(self.temp_dir, filename)
+
+    def tearDown(self):
+        if self.temp_dir and os.path.isdir(self.temp_dir):
+            shutil.rmtree(self.temp_dir)
+
+    def _test_write_file(self, content, expected, **kwargs):
+        file_path = self._test_path("abcfile")
+        write_file(file_path, content)
+        assert os.path.isfile(file_path)
+
+        with open(file_path, 'rb') as f:
+            found = f.read()
+        assert found == expected, repr(found)
+
+    def test_write_file_text(self):
+        self._test_write_file("abcüöä", b'abc\xc3\xbc\xc3\xb6\xc3\xa4')
+
+    def test_write_file_bytes(self):
+        self._test_write_file(b"ab\0c", b"ab\0c")
+
+    def test_write_newer_file(self):
+        file_path_1 = self._test_path("abcfile1.txt")
+        file_path_2 = self._test_path("abcfile2.txt")
+        write_file(file_path_1, "abc")
+        assert os.path.isfile(file_path_1)
+        write_newer_file(file_path_2, file_path_1, "xyz")
+        assert os.path.isfile(file_path_2)
+        assert os.path.getmtime(file_path_2) > os.path.getmtime(file_path_1)
+
+    def test_write_newer_file_same(self):
+        file_path = self._test_path("abcfile.txt")
+        write_file(file_path, "abc")
+        mtime = os.path.getmtime(file_path)
+        write_newer_file(file_path, file_path, "xyz")
+        assert os.path.getmtime(file_path) > mtime
+
+    def test_write_newer_file_fresh(self):
+        file_path = self._test_path("abcfile.txt")
+        assert not os.path.exists(file_path)
+        write_newer_file(file_path, file_path, "xyz")
+        assert os.path.isfile(file_path)