Transform require_numba decorator into a global variable (#245)

The require_numba as a function wrapper makes it hard to use
pytest.mark.parametrize on test functions. Following pytest
documentation, it's better to define custom decorators as global
variables.

harmonica/tests/utils.py

@@ -4,37 +4,29 @@
 #
 # This code is part of the Fatiando a Terra project (https://www.fatiando.org)
 #
+# pylint: disable=invalid-name
 """
 Decorators and useful functions for running tests
 """
 import os
 import pytest
 
+# Check if Numba is disabled
+# (if NUMBA_DISABLE_JIT is not defined, we assume Numba jit is enabled)
+NUMBA_IS_DISABLED = bool(os.environ.get("NUMBA_DISABLE_JIT", default="0") != "0")
 
-def require_numba(function): # pylint: disable=unused-argument
- """
- Function decorator for pytest: run if Numba jit is enabled
-
- Functions decorator to tell pytest to run the test function only if Numba
- jit is enabled. To disable Numba jit the environmental variable
- ```NUMBA_DISABLE_JIT``` must be set to a value different than 0.
-
- Use this decorator on test functions that involve great computational load
- and don't want to run if Numba jit is disabled. The decorated test
- functions will be run and checked if pass or fail, but won't be taken into
- account for meassuring coverage. If the test function will run Numba code,
- but doesn't involve great computational load, we reccomend using the
- ``@pytest.mark.use_numba`` instead. Therefore the test function will be run
- twice: one with Numba jit enabled, and another one with Numba jit disable
- to check coverage.
- """
- # Check if Numba is disabled
- # (if NUMBA_DISABLE_JIT is not defined, we assume Numba jit is enabled)
- numba_is_disabled = bool(os.environ.get("NUMBA_DISABLE_JIT", default="0") != "0")
-
- @pytest.mark.use_numba
- @pytest.mark.skipif(numba_is_disabled, reason="Numba jit is disabled")
- def function_wrapper():
- function()
-
- return function_wrapper
+# Decorator for pytest: run if Numba jit is enabled
+#
+# Tell pytest to run the test function only if Numba jit is enabled. To disable
+# Numba jit the environmental variable ```NUMBA_DISABLE_JIT``` must be set to
+# a value different than 0.
+#
+# Use this decorator on test functions that involve great computational load
+# and don't want to run if Numba jit is disabled. The decorated test functions
+# will be run and checked if pass or fail, but won't be taken into account for
+# meassuring coverage. If the test function will run Numba code, but doesn't
+# involve great computational load, we reccomend using the
+# ``@pytest.mark.use_numba`` instead. Therefore the test function will be run
+# twice: one with Numba jit enabled, and another one with Numba jit disable to
+# check coverage.
+require_numba = pytest.mark.skipif(NUMBA_IS_DISABLED, reason="Numba jit is disabled")