class_docstr: The CLI runner provides functionality to invoke a Click command line
  script for unittesting purposes in a isolated environment.  This only
  works in single-threaded systems without any concurrency as it changes the
  global interpreter state.
  
  :param charset: the character set for the input and output data.  This is
                  UTF-8 by default and should not be changed currently as
                  the reporting to Click only works in Python 2 properly.
  :param env: a dictionary with environment variables for overriding.
  :param echo_stdin: if this is set to `True`, then reading from stdin writes
                     to stdout.  This is useful for showing examples in
                     some circumstances.  Note that regular prompts
                     will automatically echo the input.
  :param mix_stderr: if this is set to `False`, then stdout and stderr are
                     preserved as independent streams.  This is useful for
                     Unix-philosophy apps that have predictable stdout and
                     noisy stderr, such that each may be measured
                     independently
docstr: Returns the environment overrides for invoking a script.
code: def make_env(self, overrides=None):
      """Returns the environment overrides for invoking a script."""
      rv = dict(self.env)
      if overrides:
          rv.update(overrides)
      return rv
  
imports: import contextlib
  import os
  import shlex
  import shutil
  import sys
  import tempfile
  from .None import formatting
  from .None import termui
  from .None import utils
  from ._compat import iteritems
  from ._compat import PY2
  from ._compat import string_types
label_desc: Use image node_id 3 for calling the CliRunner obj's underlying member method code with example usage: obj.make_env(overrides) and returns: rv