Print installed packages in pytest

tests/conftest.py

@@ -1,4 +1,6 @@
 import os
+import subprocess
+import sys
 
 from chainer import testing
 from chainer.testing import parameterized
@@ -9,6 +11,26 @@
 assert _pairwise_parameterize in ('never', 'always')
 
 
+def _is_pip_installed():
+    try:
+        import pip  # NOQA
+        return True
+    except ImportError:
+        return False
+
+
+def _is_in_ci():
+    ci_name = os.environ.get('CHAINER_CI', '')
+    return ci_name != ''
+
+
+def pytest_configure(config):
+    # Print installed packages
+    if _is_in_ci() and _is_pip_installed():
+        print("***** Installed packages *****", flush=True)
+        subprocess.check_call([sys.executable, '-m', 'pip', 'freeze', '--all'])
+
+
 def pytest_collection(session):
     # Perform pairwise testing.
     # TODO(kataoka): This is a tentative fix. Discuss its public interface.