add blacken to noxfile (#6795)

Author: crwilcox

packages/google-cloud-dns/noxfile.py

@@ -25,6 +25,45 @@
 )
 
 
+@nox.session(python="3.7")
+def lint(session):
+    """Run linters.
+    Returns a failure if the linters find linting errors or sufficiently
+    serious code quality issues.
+    """
+    session.install("flake8", "black", *LOCAL_DEPS)
+    session.run(
+        "black",
+        "--check",
+        "google",
+        "tests",
+        "docs",
+    )
+    session.run("flake8", "google", "tests")
+
+
+@nox.session(python="3.6")
+def blacken(session):
+    """Run black.
+    Format code to uniform standard.
+    """
+    session.install("black")
+    session.run(
+        "black",
+        "google",
+        "tests",
+        "docs",
+    )
+
+
+@nox.session(python='3.6')
+def lint_setup_py(session):
+    """Verify that setup.py is valid (including RST check)."""
+    session.install('docutils', 'Pygments')
+    session.run(
+        'python', 'setup.py', 'check', '--restructuredtext', '--strict')
+
+
 def default(session):
     """Default unit test session.
 
@@ -60,27 +99,6 @@ def unit(session):
     default(session)
 
 
-@nox.session(python='3.6')
-def lint(session):
-    """Run linters.
-
-    Returns a failure if the linters find linting errors or sufficiently
-    serious code quality issues.
-    """
-    session.install('flake8', *LOCAL_DEPS)
-    session.install('.')
-    session.run('flake8', 'google', 'tests')
-
-
-@nox.session(python='3.6')
-def lint_setup_py(session):
-    """Verify that setup.py is valid (including RST check)."""
-
-    session.install('docutils', 'Pygments')
-    session.run(
-        'python', 'setup.py', 'check', '--restructuredtext', '--strict')
-
-
 @nox.session(python='3.6')
 def cover(session):
     """Run the final coverage report.