Add some integration tests

This is mainly so we have a framework for adding specific integration
tests, e.g. for #75 (in fact IIUC, test_subdir() here exercises that
case, and it is indeed broken).

tests/integration_test.py

@@ -0,0 +1,84 @@
+"""Some things you just can't test as unit tests"""
+
+import os
+import subprocess
+import sys
+import tempfile
+import unittest
+
+
+example = """
+def main():
+    print(gcd(15, 10))
+    print(gcd(45, 12))
+
+def gcd(a, b):
+    while b:
+        a, b = b, a%b
+    return a
+"""
+
+driver = """
+from pyannotate_runtime import collect_types
+
+if __name__ == '__main__':
+    collect_types.init_types_collection()
+    with collect_types.collect():
+        main()
+    collect_types.dump_stats('type_info.json')
+"""
+
+
+class IntegrationTest(unittest.TestCase):
+
+    def setUp(self):
+        self.savedir = os.getcwd()
+        os.putenv('PYTHONPATH', self.savedir)
+        self.tempdir = tempfile.mkdtemp()
+        os.chdir(self.tempdir)
+
+    def tearDown(self):
+        os.chdir(self.savedir)
+
+    def test_simple(self):
+        with open('gcd.py', 'w') as f:
+            f.write(example)
+        with open('driver.py', 'w') as f:
+            f.write('from gcd import main\n')
+            f.write(driver)
+        subprocess.check_call([sys.executable, 'driver.py'])
+        output = subprocess.check_output([sys.executable, '-m', 'pyannotate_tools.annotations', 'gcd.py'])
+        lines = output.splitlines()
+        assert b'+    # type: () -> None' in lines
+        assert b'+    # type: (int, int) -> int' in lines
+
+    def test_package(self):
+        os.makedirs('foo')
+        with open('foo/__init__.py', 'w') as f:
+            pass
+        with open('foo/gcd.py', 'w') as f:
+            f.write(example)
+        with open('driver.py', 'w') as f:
+            f.write('from foo.gcd import main\n')
+            f.write(driver)
+        subprocess.check_call([sys.executable, 'driver.py'])
+        output = subprocess.check_output([sys.executable, '-m', 'pyannotate_tools.annotations', 'foo/gcd.py'])
+        lines = output.splitlines()
+        assert b'+    # type: () -> None' in lines
+        assert b'+    # type: (int, int) -> int' in lines
+
+    @unittest.skip("Doesn't work yet")
+    def test_subdir(self):
+        os.makedirs('foo')
+        with open('foo/gcd.py', 'w') as f:
+            f.write(example)
+        with open('driver.py', 'w') as f:
+            f.write('import sys\n')
+            f.write('sys.path.insert(0, "foo")\n')
+            f.write('from gcd import main\n')
+            f.write(driver)
+        subprocess.check_call([sys.executable, 'driver.py'])
+        output = subprocess.check_output([sys.executable, '-m', 'pyannotate_tools.annotations', 'foo/gcd.py'])
+        lines = output.splitlines()
+        assert b'+    # type: () -> None' in lines
+        assert b'+    # type: (int, int) -> int' in lines