Implement PEP 477 - Backport ensurepip (PEP 453) to 2.7

* Backports ensurepip to the 2.7 branch
* Backports some of the improved documentation to the 2.7 branch.
* Adds a private backport of the 3.x mock library as test._mock_backport
  to enable saner testing of ensurepip.

Key Differences from 3.x:

* Ensurepip does not have any Makefile integration, specifically
  it is not ran by default in the Makefile.
* There is no venv module in 2.7, so downstream distributors can
  completely disable ensurepip, ideally with a message redirecting
  to the correct way to install pip.
* To match the ``python`` command in 2.7, ensurepip will install
  the unversioned ``pip`` command as well.
* No-op and hide --default-pip and add --no-default-pip to restore
  the 3.x behavor on 2.7.
diff --git a/Lib/test/test_ensurepip.py b/Lib/test/test_ensurepip.py
new file mode 100644
index 0000000..f671ee3
--- /dev/null
+++ b/Lib/test/test_ensurepip.py
@@ -0,0 +1,352 @@
+import unittest
+import os
+import os.path
+import contextlib
+import sys
+import test._mock_backport as mock
+import test.test_support
+
+import ensurepip
+import ensurepip._uninstall
+
+# pip currently requires ssl support, so we ensure we handle
+# it being missing (http://bugs.python.org/issue19744)
+ensurepip_no_ssl = test.test_support.import_fresh_module("ensurepip",
+                                                         blocked=["ssl"])
+try:
+    import ssl
+except ImportError:
+    ssl = None
+
+    def requires_usable_pip(f):
+        deco = unittest.skip(ensurepip._MISSING_SSL_MESSAGE)
+        return deco(f)
+else:
+    def requires_usable_pip(f):
+        return f
+
+
+class TestEnsurePipVersion(unittest.TestCase):
+
+    def test_returns_version(self):
+        self.assertEqual(ensurepip._PIP_VERSION, ensurepip.version())
+
+
+class EnsurepipMixin:
+
+    def setUp(self):
+        run_pip_patch = mock.patch("ensurepip._run_pip")
+        self.run_pip = run_pip_patch.start()
+        self.addCleanup(run_pip_patch.stop)
+
+        # Avoid side effects on the actual os module
+        real_devnull = os.devnull
+        os_patch = mock.patch("ensurepip.os")
+        patched_os = os_patch.start()
+        self.addCleanup(os_patch.stop)
+        patched_os.devnull = real_devnull
+        patched_os.path = os.path
+        self.os_environ = patched_os.environ = os.environ.copy()
+
+
+class TestBootstrap(EnsurepipMixin, unittest.TestCase):
+
+    @requires_usable_pip
+    def test_basic_bootstrapping(self):
+        ensurepip.bootstrap()
+
+        self.run_pip.assert_called_once_with(
+            [
+                "install", "--no-index", "--find-links",
+                mock.ANY, "setuptools", "pip",
+            ],
+            mock.ANY,
+        )
+
+        additional_paths = self.run_pip.call_args[0][1]
+        self.assertEqual(len(additional_paths), 2)
+
+    @requires_usable_pip
+    def test_bootstrapping_with_root(self):
+        ensurepip.bootstrap(root="/foo/bar/")
+
+        self.run_pip.assert_called_once_with(
+            [
+                "install", "--no-index", "--find-links",
+                mock.ANY, "--root", "/foo/bar/",
+                "setuptools", "pip",
+            ],
+            mock.ANY,
+        )
+
+    @requires_usable_pip
+    def test_bootstrapping_with_user(self):
+        ensurepip.bootstrap(user=True)
+
+        self.run_pip.assert_called_once_with(
+            [
+                "install", "--no-index", "--find-links",
+                mock.ANY, "--user", "setuptools", "pip",
+            ],
+            mock.ANY,
+        )
+
+    @requires_usable_pip
+    def test_bootstrapping_with_upgrade(self):
+        ensurepip.bootstrap(upgrade=True)
+
+        self.run_pip.assert_called_once_with(
+            [
+                "install", "--no-index", "--find-links",
+                mock.ANY, "--upgrade", "setuptools", "pip",
+            ],
+            mock.ANY,
+        )
+
+    @requires_usable_pip
+    def test_bootstrapping_with_verbosity_1(self):
+        ensurepip.bootstrap(verbosity=1)
+
+        self.run_pip.assert_called_once_with(
+            [
+                "install", "--no-index", "--find-links",
+                mock.ANY, "-v", "setuptools", "pip",
+            ],
+            mock.ANY,
+        )
+
+    @requires_usable_pip
+    def test_bootstrapping_with_verbosity_2(self):
+        ensurepip.bootstrap(verbosity=2)
+
+        self.run_pip.assert_called_once_with(
+            [
+                "install", "--no-index", "--find-links",
+                mock.ANY, "-vv", "setuptools", "pip",
+            ],
+            mock.ANY,
+        )
+
+    @requires_usable_pip
+    def test_bootstrapping_with_verbosity_3(self):
+        ensurepip.bootstrap(verbosity=3)
+
+        self.run_pip.assert_called_once_with(
+            [
+                "install", "--no-index", "--find-links",
+                mock.ANY, "-vvv", "setuptools", "pip",
+            ],
+            mock.ANY,
+        )
+
+    @requires_usable_pip
+    def test_bootstrapping_with_regular_install(self):
+        ensurepip.bootstrap()
+        self.assertEqual(self.os_environ["ENSUREPIP_OPTIONS"], "install")
+
+    @requires_usable_pip
+    def test_bootstrapping_with_alt_install(self):
+        ensurepip.bootstrap(altinstall=True)
+        self.assertEqual(self.os_environ["ENSUREPIP_OPTIONS"], "altinstall")
+
+    @requires_usable_pip
+    def test_bootstrapping_with_default_pip(self):
+        ensurepip.bootstrap(default_pip=True)
+        self.assertNotIn("ENSUREPIP_OPTIONS", self.os_environ)
+
+    def test_altinstall_default_pip_conflict(self):
+        with self.assertRaises(ValueError):
+            ensurepip.bootstrap(altinstall=True, default_pip=True)
+        self.assertFalse(self.run_pip.called)
+
+    @requires_usable_pip
+    def test_pip_environment_variables_removed(self):
+        # ensurepip deliberately ignores all pip environment variables
+        # See http://bugs.python.org/issue19734 for details
+        self.os_environ["PIP_THIS_SHOULD_GO_AWAY"] = "test fodder"
+        ensurepip.bootstrap()
+        self.assertNotIn("PIP_THIS_SHOULD_GO_AWAY", self.os_environ)
+
+    @requires_usable_pip
+    def test_pip_config_file_disabled(self):
+        # ensurepip deliberately ignores the pip config file
+        # See http://bugs.python.org/issue20053 for details
+        ensurepip.bootstrap()
+        self.assertEqual(self.os_environ["PIP_CONFIG_FILE"], os.devnull)
+
+
+@contextlib.contextmanager
+def fake_pip(version=ensurepip._PIP_VERSION):
+    if version is None:
+        pip = None
+    else:
+        class FakePip():
+            __version__ = version
+        pip = FakePip()
+    sentinel = object()
+    orig_pip = sys.modules.get("pip", sentinel)
+    sys.modules["pip"] = pip
+    try:
+        yield pip
+    finally:
+        if orig_pip is sentinel:
+            del sys.modules["pip"]
+        else:
+            sys.modules["pip"] = orig_pip
+
+
+class TestUninstall(EnsurepipMixin, unittest.TestCase):
+
+    def test_uninstall_skipped_when_not_installed(self):
+        with fake_pip(None):
+            ensurepip._uninstall_helper()
+        self.assertFalse(self.run_pip.called)
+
+    def test_uninstall_skipped_with_warning_for_wrong_version(self):
+        with fake_pip("not a valid version"):
+            with test.test_support.captured_stderr() as stderr:
+                ensurepip._uninstall_helper()
+        warning = stderr.getvalue().strip()
+        self.assertIn("only uninstall a matching version", warning)
+        self.assertFalse(self.run_pip.called)
+
+    @requires_usable_pip
+    def test_uninstall(self):
+        with fake_pip():
+            ensurepip._uninstall_helper()
+
+        self.run_pip.assert_called_once_with(
+            ["uninstall", "-y", "pip", "setuptools"]
+        )
+
+    @requires_usable_pip
+    def test_uninstall_with_verbosity_1(self):
+        with fake_pip():
+            ensurepip._uninstall_helper(verbosity=1)
+
+        self.run_pip.assert_called_once_with(
+            ["uninstall", "-y", "-v", "pip", "setuptools"]
+        )
+
+    @requires_usable_pip
+    def test_uninstall_with_verbosity_2(self):
+        with fake_pip():
+            ensurepip._uninstall_helper(verbosity=2)
+
+        self.run_pip.assert_called_once_with(
+            ["uninstall", "-y", "-vv", "pip", "setuptools"]
+        )
+
+    @requires_usable_pip
+    def test_uninstall_with_verbosity_3(self):
+        with fake_pip():
+            ensurepip._uninstall_helper(verbosity=3)
+
+        self.run_pip.assert_called_once_with(
+            ["uninstall", "-y", "-vvv", "pip", "setuptools"]
+        )
+
+    @requires_usable_pip
+    def test_pip_environment_variables_removed(self):
+        # ensurepip deliberately ignores all pip environment variables
+        # See http://bugs.python.org/issue19734 for details
+        self.os_environ["PIP_THIS_SHOULD_GO_AWAY"] = "test fodder"
+        with fake_pip():
+            ensurepip._uninstall_helper()
+        self.assertNotIn("PIP_THIS_SHOULD_GO_AWAY", self.os_environ)
+
+    @requires_usable_pip
+    def test_pip_config_file_disabled(self):
+        # ensurepip deliberately ignores the pip config file
+        # See http://bugs.python.org/issue20053 for details
+        with fake_pip():
+            ensurepip._uninstall_helper()
+        self.assertEqual(self.os_environ["PIP_CONFIG_FILE"], os.devnull)
+
+
+class TestMissingSSL(EnsurepipMixin, unittest.TestCase):
+
+    def setUp(self):
+        sys.modules["ensurepip"] = ensurepip_no_ssl
+
+        @self.addCleanup
+        def restore_module():
+            sys.modules["ensurepip"] = ensurepip
+        super(TestMissingSSL, self).setUp()
+
+    def test_bootstrap_requires_ssl(self):
+        self.os_environ["PIP_THIS_SHOULD_STAY"] = "test fodder"
+        with self.assertRaisesRegexp(RuntimeError, "requires SSL/TLS"):
+            ensurepip_no_ssl.bootstrap()
+        self.assertFalse(self.run_pip.called)
+        self.assertIn("PIP_THIS_SHOULD_STAY", self.os_environ)
+
+    def test_uninstall_requires_ssl(self):
+        self.os_environ["PIP_THIS_SHOULD_STAY"] = "test fodder"
+        with self.assertRaisesRegexp(RuntimeError, "requires SSL/TLS"):
+            with fake_pip():
+                ensurepip_no_ssl._uninstall_helper()
+        self.assertFalse(self.run_pip.called)
+        self.assertIn("PIP_THIS_SHOULD_STAY", self.os_environ)
+
+    def test_main_exits_early_with_warning(self):
+        with test.test_support.captured_stderr() as stderr:
+            ensurepip_no_ssl._main(["--version"])
+        warning = stderr.getvalue().strip()
+        self.assertTrue(warning.endswith("requires SSL/TLS"), warning)
+        self.assertFalse(self.run_pip.called)
+
+# Basic testing of the main functions and their argument parsing
+
+EXPECTED_VERSION_OUTPUT = "pip " + ensurepip._PIP_VERSION
+
+
+class TestBootstrappingMainFunction(EnsurepipMixin, unittest.TestCase):
+
+    @requires_usable_pip
+    def test_bootstrap_version(self):
+        with test.test_support.captured_stderr() as stderr:
+            with self.assertRaises(SystemExit):
+                ensurepip._main(["--version"])
+        result = stderr.getvalue().strip()
+        self.assertEqual(result, EXPECTED_VERSION_OUTPUT)
+        self.assertFalse(self.run_pip.called)
+
+    @requires_usable_pip
+    def test_basic_bootstrapping(self):
+        ensurepip._main([])
+
+        self.run_pip.assert_called_once_with(
+            [
+                "install", "--no-index", "--find-links",
+                mock.ANY, "setuptools", "pip",
+            ],
+            mock.ANY,
+        )
+
+        additional_paths = self.run_pip.call_args[0][1]
+        self.assertEqual(len(additional_paths), 2)
+
+
+class TestUninstallationMainFunction(EnsurepipMixin, unittest.TestCase):
+
+    def test_uninstall_version(self):
+        with test.test_support.captured_stderr() as stderr:
+            with self.assertRaises(SystemExit):
+                ensurepip._uninstall._main(["--version"])
+        result = stderr.getvalue().strip()
+        self.assertEqual(result, EXPECTED_VERSION_OUTPUT)
+        self.assertFalse(self.run_pip.called)
+
+    @requires_usable_pip
+    def test_basic_uninstall(self):
+        with fake_pip():
+            ensurepip._uninstall._main([])
+
+        self.run_pip.assert_called_once_with(
+            ["uninstall", "-y", "pip", "setuptools"]
+        )
+
+
+if __name__ == "__main__":
+    test.test_support.run_unittest(__name__)