Simplify the testing of the toml extra, fixing #1084

CHANGES.rst

@@ -38,12 +38,16 @@ Unreleased
 - Combining files on Windows across drives how works properly, fixing `issue
   577`_.  Thanks, `Valentine Lab <pr1080_>`_.
 
+- Fix an obscure warning from deep in the _decimal module, as reported in
+  `issue 1084`_.
+
 - Update to support Python 3.10 alphas in progress, including `PEP 626: Precise
   line numbers for debugging and other tools <pep626_>`_.
 
 .. _issue 577: https://github.com/nedbat/coveragepy/issues/577
 .. _issue 732: https://github.com/nedbat/coveragepy/issues/732
 .. _issue 922: https://github.com/nedbat/coveragepy/issues/922
+.. _issue 1084: https://github.com/nedbat/coveragepy/issues/1084
 .. _issue 1086: https://github.com/nedbat/coveragepy/issues/1086
 .. _issue 1090: https://github.com/nedbat/coveragepy/issues/1090
 .. _pr1080: https://github.com/nedbat/coveragepy/pull/1080

coverage/tomlconfig.py

@@ -11,6 +11,12 @@
 from coverage.backward import configparser, path_types
 from coverage.misc import CoverageException, substitute_variables
 
+# TOML support is an install-time extra option.
+try:
+    import toml
+except ImportError:         # pragma: not covered
+    toml = None
+
 
 class TomlDecodeError(Exception):
     """An exception class that exists even when toml isn't installed."""
@@ -29,8 +35,6 @@ def __init__(self, our_file):
         self.data = None
 
     def read(self, filenames):
-        from coverage.optional import toml
-
         # RawConfigParser takes a filename or list of filenames, but we only
         # ever call this with a single filename.
         assert isinstance(filenames, path_types)

tests/helpers.py

@@ -10,6 +10,7 @@
 import subprocess
 import sys
 
+import mock
 from unittest_mixins import ModuleCleaner
 
 from coverage import env
@@ -203,3 +204,21 @@ def arcs_to_arcz_repr(arcs):
         line += _arcs_to_arcz_repr_one(b)
         repr_list.append(line)
     return "\n".join(repr_list) + "\n"
+
+
+def without_module(using_module, missing_module_name):
+    """
+    Hide a module for testing.
+
+    Use this in a test function to make an optional module unavailable during
+    the test::
+
+        with without_module(product.something, 'toml'):
+            use_toml_somehow()
+
+    Arguments:
+        using_module: a module in which to hide `missing_module_name`.
+        missing_module_name (str): the name of the module to hide.
+
+    """
+    return mock.patch.object(using_module, missing_module_name, None)

tests/test_config.py

@@ -10,9 +10,9 @@
 
 import coverage
 from coverage.misc import CoverageException
-import coverage.optional
 
 from tests.coveragetest import CoverageTest, UsingModulesMixin
+from tests.helpers import without_module
 
 
 class ConfigTest(CoverageTest):
@@ -712,15 +712,15 @@ def test_nocoveragerc_file_when_specified(self):
 
     def test_no_toml_installed_no_toml(self):
         # Can't read a toml file that doesn't exist.
-        with coverage.optional.without('toml'):
+        with without_module(coverage.tomlconfig, 'toml'):
             msg = "Couldn't read 'cov.toml' as a config file"
             with self.assertRaisesRegex(CoverageException, msg):
                 coverage.Coverage(config_file="cov.toml")
 
     def test_no_toml_installed_explicit_toml(self):
         # Can't specify a toml config file if toml isn't installed.
         self.make_file("cov.toml", "# A toml file!")
-        with coverage.optional.without('toml'):
+        with without_module(coverage.tomlconfig, 'toml'):
             msg = "Can't read 'cov.toml' without TOML support"
             with self.assertRaisesRegex(CoverageException, msg):
                 coverage.Coverage(config_file="cov.toml")
@@ -732,7 +732,7 @@ def test_no_toml_installed_pyproject_toml(self):
             [tool.coverage.run]
             xyzzy = 17
             """)
-        with coverage.optional.without('toml'):
+        with without_module(coverage.tomlconfig, 'toml'):
             msg = "Can't read 'pyproject.toml' without TOML support"
             with self.assertRaisesRegex(CoverageException, msg):
                 coverage.Coverage()
@@ -744,7 +744,7 @@ def test_no_toml_installed_pyproject_no_coverage(self):
             [tool.something]
             xyzzy = 17
             """)
-        with coverage.optional.without('toml'):
+        with without_module(coverage.tomlconfig, 'toml'):
             cov = coverage.Coverage()
             # We get default settings:
             self.assertFalse(cov.config.timid)

tests/test_testing.py

@@ -12,14 +12,16 @@
 import pytest
 
 import coverage
+from coverage import tomlconfig
 from coverage.backunittest import TestCase, unittest
 from coverage.files import actual_path
 from coverage.misc import StopEverything
-import coverage.optional
 
 from tests.coveragetest import CoverageTest, convert_skip_exceptions
-from tests.helpers import arcs_to_arcz_repr, arcz_to_arcs
-from tests.helpers import CheckUniqueFilenames, re_lines, re_line
+from tests.helpers import (
+    arcs_to_arcz_repr, arcz_to_arcs,
+    CheckUniqueFilenames, re_lines, re_line, without_module,
+)
 
 
 def test_xdist_sys_path_nuttiness_is_fixed():
@@ -323,12 +325,11 @@ def _same_python_executable(e1, e2):
     return False                                        # pragma: only failure
 
 
-def test_optional_without():
-    # pylint: disable=reimported
-    from coverage.optional import toml as toml1
-    with coverage.optional.without('toml'):
-        from coverage.optional import toml as toml2
-    from coverage.optional import toml as toml3
+def test_without_module():
+    toml1 = tomlconfig.toml
+    with without_module(tomlconfig, 'toml'):
+        toml2 = tomlconfig.toml
+    toml3 = tomlconfig.toml
 
     assert toml1 is toml3 is not None
     assert toml2 is None