Test current initial-refresh behavior

This adds tests of the initial refresh that is attempted
automatically on import. All the refresh tests prior to this point
test subsequent refreshes. Those tests are kept, and new ones are
added that simulate the condition of not having yet done the
initial refresh by setting Git.GIT_PYTHON_GIT_EXECUTABLE to None.

Some current behavior these tests assert may change for gitpython-developers#1808.

test/test_git.py

@@ -6,6 +6,7 @@
 import contextlib
 import gc
 import inspect
+import io
 import logging
 import os
 import os.path as osp
@@ -329,6 +330,80 @@ def test_cmd_override(self):
         ):
             self.assertRaises(GitCommandNotFound, self.git.version)
 
+    def test_git_exc_name_is_git(self):
+        self.assertEqual(self.git.git_exec_name, "git")
+
+    @ddt.data(("0",), ("q",), ("quiet",), ("s",), ("silence",), ("n",), ("none",))
+    def test_initial_refresh_from_bad_git_path_env_quiet(self, case):
+        """In "q" mode, bad initial path sets "git" and is quiet."""
+        (mode,) = case
+        set_vars = {
+            "GIT_PYTHON_GIT_EXECUTABLE": str(Path("yada").absolute()),  # Any bad path.
+            "GIT_PYTHON_REFRESH": mode,
+        }
+        with _rollback_refresh():
+            type(self.git).GIT_PYTHON_GIT_EXECUTABLE = None  # Simulate startup.
+
+            with mock.patch.dict(os.environ, set_vars):
+                refresh()
+                self.assertEqual(self.git.GIT_PYTHON_GIT_EXECUTABLE, "git")
+
+    @ddt.data(("1",), ("w",), ("warn",), ("warning",))
+    def test_initial_refresh_from_bad_git_path_env_warn(self, case):
+        """In "w" mode, bad initial path sets "git" and warns."""
+        (mode,) = case
+        env_vars = {
+            "GIT_PYTHON_GIT_EXECUTABLE": str(Path("yada").absolute()),  # Any bad path.
+            "GIT_PYTHON_REFRESH": mode,
+        }
+        with _rollback_refresh():
+            type(self.git).GIT_PYTHON_GIT_EXECUTABLE = None  # Simulate startup.
+
+            with mock.patch.dict(os.environ, env_vars):
+                with contextlib.redirect_stdout(io.StringIO()) as out:
+                    refresh()
+                self.assertRegex(out.getvalue(), r"\AWARNING: Bad git executable.\n")
+                self.assertEqual(self.git.GIT_PYTHON_GIT_EXECUTABLE, "git")
+
+    @ddt.data(("2",), ("r",), ("raise",), ("e",), ("error",))
+    def test_initial_refresh_from_bad_git_path_env_error(self, case):
+        """In "e" mode, bad initial path raises an exception."""
+        (mode,) = case
+        env_vars = {
+            "GIT_PYTHON_GIT_EXECUTABLE": str(Path("yada").absolute()),  # Any bad path.
+            "GIT_PYTHON_REFRESH": mode,
+        }
+        with _rollback_refresh():
+            type(self.git).GIT_PYTHON_GIT_EXECUTABLE = None  # Simulate startup.
+
+            with mock.patch.dict(os.environ, env_vars):
+                with self.assertRaisesRegex(ImportError, r"\ABad git executable.\n"):
+                    refresh()
+
+    def test_initial_refresh_from_good_absolute_git_path_env(self):
+        """Good initial absolute path from environment is set."""
+        absolute_path = shutil.which("git")
+
+        with _rollback_refresh():
+            type(self.git).GIT_PYTHON_GIT_EXECUTABLE = None  # Simulate startup.
+
+            with mock.patch.dict(os.environ, {"GIT_PYTHON_GIT_EXECUTABLE": absolute_path}):
+                refresh()
+                self.assertEqual(self.git.GIT_PYTHON_GIT_EXECUTABLE, absolute_path)
+
+    def test_initial_refresh_from_good_relative_git_path_env(self):
+        """Good initial relative path from environment is kept relative and set."""
+        with _rollback_refresh():
+            # Set the fallback to a string that wouldn't work and isn't "git", so we are
+            # more likely to detect if "git" is not set from the environment variable.
+            with mock.patch.object(type(self.git), "git_exec_name", ""):
+                type(self.git).GIT_PYTHON_GIT_EXECUTABLE = None  # Simulate startup.
+
+                # Now observe if setting the environment variable to "git" takes effect.
+                with mock.patch.dict(os.environ, {"GIT_PYTHON_GIT_EXECUTABLE": "git"}):
+                    refresh()
+                    self.assertEqual(self.git.GIT_PYTHON_GIT_EXECUTABLE, "git")
+
     def test_refresh_from_bad_absolute_git_path_env(self):
         """Bad absolute path from environment is reported and not set."""
         absolute_path = str(Path("yada").absolute())
@@ -365,7 +440,7 @@ def test_refresh_from_good_absolute_git_path_env(self):
     def test_refresh_from_good_relative_git_path_env(self):
         """Good relative path from environment is kept relative and set."""
         with _rollback_refresh():
-            # Set a string that wouldn't work and isn't "git".
+            # Set as the executable name a string that wouldn't work and isn't "git".
             type(self.git).GIT_PYTHON_GIT_EXECUTABLE = ""
 
             # Now observe if setting the environment variable to "git" takes effect.