Added mypy for static type checking

2 files changed, 45 insertions, 22 deletions

diff --git a/tests/test_cli.py b/tests/test_cli.py
index 7cf7ed4..1cd92c2 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -4,41 +4,37 @@ Unit tests for CLI entry points.
 
 from __future__ import print_function
 
-import unittest
-import sys
 import functools
-from contextlib import contextmanager
-
+import io
 import os
-from io import StringIO, BytesIO
+import sys
+import typing
+import unittest
+from contextlib import contextmanager, redirect_stdout, redirect_stderr
 
 import rsa
 import rsa.cli
 import rsa.util
 
 
-def make_buffer() -> StringIO:
-    buf = StringIO()
-    buf.buffer = BytesIO()
-    return buf
+@contextmanager
+def captured_output() -> typing.Generator:
+    """Captures output to stdout and stderr"""
 
+    # According to mypy, we're not supposed to change buf_out.buffer.
+    # However, this is just a test, and it works, hence the 'type: ignore'.
+    buf_out = io.StringIO()
+    buf_out.buffer = io.BytesIO()  # type: ignore
 
-def get_bytes_out(out: StringIO) -> bytes:
-    # Python 3.x writes 'bytes' to stdout.buffer
-    return out.buffer.getvalue()
+    buf_err = io.StringIO()
+    buf_err.buffer = io.BytesIO()  # type: ignore
 
+    with redirect_stdout(buf_out), redirect_stderr(buf_err):
+        yield buf_out, buf_err
 
-@contextmanager
-def captured_output():
-    """Captures output to stdout and stderr"""
 
-    new_out, new_err = make_buffer(), make_buffer()
-    old_out, old_err = sys.stdout, sys.stderr
-    try:
-        sys.stdout, sys.stderr = new_out, new_err
-        yield new_out, new_err
-    finally:
-        sys.stdout, sys.stderr = old_out, old_err
+def get_bytes_out(buf) -> bytes:
+    return buf.buffer.getvalue()
 
 
 @contextmanager
diff --git a/tests/test_mypy.py b/tests/test_mypy.py
new file mode 100644
index 0000000..c2a9745
--- /dev/null
+++ b/tests/test_mypy.py
@@ -0,0 +1,27 @@
+import pathlib
+import unittest
+
+import mypy.api
+
+test_modules = ['rsa', 'tests']
+
+
+class MypyRunnerTest(unittest.TestCase):
+    def test_run_mypy(self):
+        proj_root = pathlib.Path(__file__).parent.parent
+        args = ['--incremental', '--ignore-missing-imports'] + [str(proj_root / dirname) for dirname
+                                                                in test_modules]
+
+        result = mypy.api.run(args)
+
+        stdout, stderr, status = result
+
+        messages = []
+        if stderr:
+            messages.append(stderr)
+        if stdout:
+            messages.append(stdout)
+        if status:
+            messages.append('Mypy failed with status %d' % status)
+        if messages:
+            self.fail('\n'.join(['Mypy errors:'] + messages))