tests: pin minimum dependency versions under Python 3.6 (#680)

Also, pin 2.7-compatible version of 'googleapis-common-protos' under 2.7

Closes #679.

Author: tseaver

packages/google-cloud-ndb/noxfile.py

@@ -18,6 +18,7 @@
 """
 
 import os
+import pathlib
 import shutil
 
 import nox
@@ -28,6 +29,7 @@
 ALL_INTERPRETERS = ("2.7", "3.6", "3.7", "3.8", "3.9")
 PY3_INTERPRETERS = ("3.6", "3.7", "3.8", "3.9")
 MAJOR_INTERPRETERS = ("2.7", "3.8")
+CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
 
 BLACK_VERSION = "black==20.8b1"
 
@@ -38,10 +40,13 @@ def get_path(*names):
 
 @nox.session(py=ALL_INTERPRETERS)
 def unit(session):
+    constraints_path = str(
+        CURRENT_DIRECTORY / "testing" / f"constraints-{session.python}.txt"
+    )
     # Install all dependencies.
     session.install("pytest", "pytest-cov")
     session.install("mock")
-    session.install("-e", ".")
+    session.install("-e", ".", "-c", constraints_path)
     # This variable is used to skip coverage by Python version
     session.env["PY_VERSION"] = session.python[0]
     # Run py.test against the unit tests.
@@ -159,6 +164,9 @@ def doctest(session):
 @nox.session(py=MAJOR_INTERPRETERS)
 def system(session):
     """Run the system test suite."""
+    constraints_path = str(
+        CURRENT_DIRECTORY / "testing" / f"constraints-{session.python}.txt"
+    )
     system_test_path = get_path("tests", "system.py")
     system_test_folder_path = os.path.join("tests", "system")
 
@@ -182,7 +190,7 @@ def system(session):
     for local_dep in LOCAL_DEPS:
         session.install(local_dep)
     session.install("-e", get_path("test_utils", "test_utils"))
-    session.install("-e", ".")
+    session.install("-e", ".", "-c", constraints_path)
 
     # Run py.test against the system tests.
     if system_test_exists:

packages/google-cloud-ndb/testing/constraints-2.7.txt

@@ -0,0 +1,2 @@
+googleapis-common-protos >= 1.6.0, < 1.53dev
+

packages/google-cloud-ndb/testing/constraints-3.10.txt

@@ -0,0 +1,9 @@
+# This constraints file is used to check that lower bounds
+# are correct in setup.py
+# List *all* library dependencies and extras in this file.
+# Pin the version to the lower bound.
+#
+# e.g., if setup.py has "foo >= 1.14.0, < 2.0.0dev",
+# Then this file should have foo==1.14.0
+googleapis-common-protos==1.6.0
+google-cloud-datastore==1.7.0