How to use the conda.common.io.env_var function in conda

with env_var("CONDA_JSON", "yes", reset_context):
            with captured() as c:
                conda_exception_handler(_raise_helper, exc)

        json_obj = json.loads(c.stdout)
        assert not c.stderr
        assert json_obj['exception_type'] == ""
        assert json_obj['exception_name'] == 'MD5MismatchError'
        assert json_obj['message'] == text_type(exc)
        assert json_obj['error'] == repr(exc)
        assert json_obj['url'] == url
        assert json_obj['target_full_path'] == target_full_path
        assert json_obj['expected_md5sum'] == expected_md5sum
        assert json_obj['actual_md5sum'] == actual_md5sum

        with env_var("CONDA_JSON", "no", reset_context):
            with captured() as c:
                conda_exception_handler(_raise_helper, exc)

        assert not c.stdout
        assert c.stderr.strip() == dals("""
        MD5MismatchError: Conda detected a mismatch between the expected content and downloaded content

def test_create_advanced_pip(self):
        with make_temp_envs_dir() as envs_dir:
            with env_var('CONDA_ENVS_DIRS', envs_dir, reset_context):
                env_name = str(uuid4())[:8]
                prefix = join(envs_dir, env_name)
                python_path = join(prefix, PYTHON_BINARY)

                run_command(Commands.CREATE, env_name,
                            utils.support_file('advanced-pip/environment.yml'))
                assert exists(python_path)
                assert_package_is_installed(prefix, 'argh', exact=False, pip=True)
                assert_package_is_installed(prefix, 'module-to-install-in-editable-mode', exact=False, pip=True)
                try:
                    assert_package_is_installed(prefix, 'six', exact=False, pip=True)
                except AssertionError:
                    # six may now be conda-installed because of packaging changes
                    assert_package_is_installed(prefix, 'six', exact=False, pip=False)
                assert_package_is_installed(prefix, 'xmltodict-0.10.2-', exact=True, pip=True)

def test_prefix_cli_flag(self):
        envs_dirs = (join(self.prefix, 'first-envs-dir'), join(self.prefix, 'seconds-envs-dir'))
        with env_var('CONDA_ENVS_DIRS', os.pathsep.join(envs_dirs), stack_callback=conda_tests_ctxt_mgmt_def_pol):

            # even if prefix doesn't exist, it can be a target prefix
            reset_context((), argparse_args=AttrDict(prefix='./blarg', func='create'))
            target_prefix = join(os.getcwd(), 'blarg')
            assert context.target_prefix == target_prefix
            assert not isdir(target_prefix)

def test_pinned_specs():
    # Test pinned specs environment variable
    specs_str_1 = ("numpy 1.11", "python >3")
    specs_1 = tuple(MatchSpec(spec_str, optional=True) for spec_str in specs_str_1)
    with env_var('CONDA_PINNED_PACKAGES', '&'.join(specs_str_1), reset_context):
        pinned_specs = get_pinned_specs("/none")
        assert pinned_specs == specs_1
        assert pinned_specs != specs_str_1

    # Test pinned specs conda environment file
    specs_str_2 = ("scipy ==0.14.2", "openjdk >=8")
    specs_2 = tuple(MatchSpec(spec_str, optional=True) for spec_str in specs_str_2)

    with tempdir() as td:
        mkdir_p(join(td, 'conda-meta'))
        with open(join(td, 'conda-meta', 'pinned'), 'w') as fh:
            fh.write("\n".join(specs_str_2))
            fh.write("\n")
        pinned_specs = get_pinned_specs(td)
        assert pinned_specs == specs_2
        assert pinned_specs != specs_str_2

def test_MD5MismatchError(self):
        url = "https://download.url/path/to/file.tar.bz2"
        target_full_path = "/some/path/on/disk/another-name.tar.bz2"
        expected_md5sum = "abc123"
        actual_md5sum = "deadbeef"
        exc = MD5MismatchError(url, target_full_path, expected_md5sum, actual_md5sum)
        with env_var("CONDA_JSON", "yes", reset_context):
            with captured() as c:
                conda_exception_handler(_raise_helper, exc)

        json_obj = json.loads(c.stdout)
        assert not c.stderr
        assert json_obj['exception_type'] == ""
        assert json_obj['exception_name'] == 'MD5MismatchError'
        assert json_obj['message'] == text_type(exc)
        assert json_obj['error'] == repr(exc)
        assert json_obj['url'] == url
        assert json_obj['target_full_path'] == target_full_path
        assert json_obj['expected_md5sum'] == expected_md5sum
        assert json_obj['actual_md5sum'] == actual_md5sum

        with env_var("CONDA_JSON", "no", reset_context):
            with captured() as c:

def test_simple_install_uninstall(self, prefix_specified):
        prefix_specified.__get__ = Mock(return_value=False)

        # >> simple progression install then uninstall <<
        run_command(Commands.INSTALL, self.prefix, "-c conda-test spiffy-test-app")
        assert not package_is_installed(self.prefix, "spiffy-test-app")
        assert isfile(self.exe_file(self.prefix, 'spiffy-test-app'))
        assert package_is_installed(self.preferred_env_prefix, "spiffy-test-app")
        with env_var('YABBA-DABBA', 'doo'):
            stdout, stderr, rc = subprocess_call(self.exe_file(self.prefix, 'spiffy-test-app'))
        assert not stderr
        assert rc == 0
        json_d = json.loads(stdout)
        assert json_d['YABBA-DABBA'] == 'doo'

        run_command(Commands.INSTALL, self.prefix, "-c conda-test uses-spiffy-test-app")
        assert not package_is_installed(self.prefix, "uses-spiffy-test-app")
        assert package_is_installed(self.preferred_env_prefix, "uses-spiffy-test-app")

        run_command(Commands.REMOVE, self.prefix, "uses-spiffy-test-app")
        assert not package_is_installed(self.preferred_env_prefix, "uses-spiffy-test-app")

        run_command(Commands.REMOVE, self.prefix, "spiffy-test-app")
        assert not package_is_installed(self.prefix, "spiffy-test-app")
        assert not isfile(self.exe_file(self.prefix, 'spiffy-test-app'))

def test_dont_remove_conda_2(self):
        # regression test for #6904
        pkgs_dirs = context.pkgs_dirs
        prefix = make_temp_prefix()
        with env_var('CONDA_ROOT_PREFIX', prefix, reset_context):
            with env_var('CONDA_PKGS_DIRS', ','.join(pkgs_dirs), reset_context):
                with make_temp_env(prefix=prefix):
                    stdout, stderr = run_command(Commands.INSTALL, prefix, "conda")
                    assert package_is_installed(prefix, "conda")
                    assert package_is_installed(prefix, "pycosat")

                    with pytest.raises(CondaMultiError) as exc:
                        run_command(Commands.REMOVE, prefix, 'pycosat')

                    assert any(isinstance(e, RemoveError) for e in exc.value.errors)
                    assert package_is_installed(prefix, "conda")
                    assert package_is_installed(prefix, "pycosat")

                    with pytest.raises(CondaMultiError) as exc:
                        run_command(Commands.REMOVE, prefix, 'conda')

                    assert any(isinstance(e, RemoveError) for e in exc.value.errors)

def get_index_cuda(subdir=context.subdir):
    with open(join(dirname(__file__), 'data', 'index.json')) as fi:
        packages = json.load(fi)
        repodata = {
            "info": {
                "subdir": subdir,
                "arch": context.arch_name,
                "platform": context.platform,
            },
            "packages": packages,
        }

    channel = Channel('https://conda.anaconda.org/channel-1/%s' % subdir)
    sd = SubdirData(channel)
    with env_var("CONDA_ADD_PIP_AS_PYTHON_DEPENDENCY", "false", reset_context):
        sd._process_raw_repodata_str(json.dumps(repodata))
    sd._loaded = True
    SubdirData._cache_[channel.url(with_credentials=True)] = sd

    index = {prec: prec for prec in sd._package_records}

    add_feature_records_legacy(index)
    r = Resolve(index, channels=(channel,))
    return index, r

def test_dont_remove_conda_2(self):
        # regression test for #6904
        pkgs_dirs = context.pkgs_dirs
        prefix = make_temp_prefix()
        with env_var('CONDA_ROOT_PREFIX', prefix, reset_context):
            with env_var('CONDA_PKGS_DIRS', ','.join(pkgs_dirs), reset_context):
                with make_temp_env(prefix=prefix):
                    stdout, stderr = run_command(Commands.INSTALL, prefix, "conda")
                    assert package_is_installed(prefix, "conda")
                    assert package_is_installed(prefix, "pycosat")

                    with pytest.raises(CondaMultiError) as exc:
                        run_command(Commands.REMOVE, prefix, 'pycosat')

                    assert any(isinstance(e, RemoveError) for e in exc.value.errors)
                    assert package_is_installed(prefix, "conda")
                    assert package_is_installed(prefix, "pycosat")

                    with pytest.raises(CondaMultiError) as exc:
                        run_command(Commands.REMOVE, prefix, 'conda')

def test_CondaFileNotFoundError(self):
        filename = "Groot"
        exc = PathNotFoundError(filename)
        with env_var("CONDA_JSON", "yes", reset_context):
            with captured() as c:
                conda_exception_handler(_raise_helper, exc)

        json_obj = json.loads(c.stdout)
        assert not c.stderr
        assert json_obj['exception_type'] == ""
        assert json_obj['exception_name'] == 'PathNotFoundError'
        assert json_obj['message'] == text_type(exc)
        assert json_obj['error'] == repr(exc)

        with env_var("CONDA_JSON", "no", reset_context):
            with captured() as c:
                conda_exception_handler(_raise_helper, exc)

        assert not c.stdout
        assert c.stderr.strip() == "PathNotFoundError: Groot"