Refactor to parse version spec

Simplify one more time down to a single version comparison helper that
parses a package spec string and compares that spec to the currently
installed package.

src/metpy/testing.py

@@ -10,6 +10,7 @@
 import contextlib
 import functools
 import importlib
+import re
 
 import numpy as np
 import numpy.testing
@@ -24,40 +25,49 @@
 from .units import units
 
 
-def module_version_before(modname, ver):
-    """Return whether the active module is before a certain version.
+def module_version_check(version_spec):
+    """Return comparison between the active module and a requested version number.
 
     Parameters
     ----------
-    modname : str
-        The module name to import
-    ver : str
-        The version string for a certain release
+    version_spec : str
+        Module version specification to validate against installed package. Must take the form
+        of `f'{module_name}{comparison_operator}{version_number}'` where `comparison_operator`
+        must be one of `['==', '=', '!=', '<', '<=', '>', '>=']`.
 
     Returns
     -------
-        bool : whether the current version was released before the passed in one
+        bool : Whether the installed package validates against the provided specification
     """
-    module = importlib.import_module(modname)
-    return Version(module.__version__) < Version(ver)
+    comparison_operators = {
+        '==': lambda x, y: x == y, '=': lambda x, y: x == y, '!=': lambda x, y: x != y,
+        '<': lambda x, y: x < y, '<=': lambda x, y: x <= y,
+        '>': lambda x, y: x > y, '>=': lambda x, y: x >= y,
+    }
 
+    # Match version_spec for groups of module name,
+    # comparison operator, and requested module version
+    pattern = re.compile(r'(\w+)\s*([<>!=]+)\s*([\d.]+)')
+    match = pattern.match(version_spec)
 
-def module_version_equal(modname, ver):
-    """Return whether the active module is equal to a certain version.
+    if match:
+        module_name = match.group(1)
+        comparison = match.group(2)
+        version_number = match.group(3)
+    else:
+        raise ValueError('No valid version specification string matched.')
 
-    Parameters
-    ----------
-    modname : str
-        The module name to import
-    ver : str
-        The version string for a certain release
+    module = importlib.import_module(module_name)
 
-    Returns
-    -------
-        bool : whether the current version is equal to the passed in one
-    """
-    module = importlib.import_module(modname)
-    return Version(module.__version__) == Version(ver)
+    installed_version = Version(module.__version__)
+    specified_version = Version(version_number)
+
+    try:
+        return comparison_operators[comparison](installed_version, specified_version)
+    except KeyError:
+        raise ValueError(
+            "Comparison operator not one of ['==', '=', '!=', '<', '<=', '>', '>=']."
+        ) from None
 
 
 def needs_module(module):

tests/calc/test_indices.py

@@ -13,7 +13,7 @@
                         mean_pressure_weighted, precipitable_water, significant_tornado,
                         supercell_composite, weighted_continuous_average)
 from metpy.testing import (assert_almost_equal, assert_array_almost_equal, get_upper_air_data,
-                           module_version_before)
+                           module_version_check)
 from metpy.units import concatenate, units
 
 
@@ -131,7 +131,7 @@ def test_weighted_continuous_average():
     assert_almost_equal(v, 6.900543760612305 * units('m/s'), 7)
 
 
-@pytest.mark.xfail(condition=module_version_before('pint', '0.21'), reason='hgrecco/pint#1593')
+@pytest.mark.xfail(condition=module_version_check('pint<0.21'), reason='hgrecco/pint#1593')
 def test_weighted_continuous_average_temperature():
     """Test pressure-weighted mean temperature function with vertical interpolation."""
     data = get_upper_air_data(datetime(2016, 5, 22, 0), 'DDC')

tests/plots/test_declarative.py

@@ -20,7 +20,7 @@
 from metpy.io.metar import parse_metar_file
 from metpy.plots import (ArrowPlot, BarbPlot, ContourPlot, FilledContourPlot, ImagePlot,
                          MapPanel, PanelContainer, PlotGeometry, PlotObs, RasterPlot)
-from metpy.testing import module_version_before, needs_cartopy
+from metpy.testing import module_version_check, needs_cartopy
 from metpy.units import units
 
 
@@ -336,7 +336,7 @@ def test_declarative_contour_cam():
 
 @pytest.mark.mpl_image_compare(
     remove_text=True,
-    tolerance=3.71 if module_version_before('matplotlib', '3.8') else 0.74)
+    tolerance=3.71 if module_version_check('matplotlib<3.8') else 0.74)
 @needs_cartopy
 def test_declarative_contour_options():
     """Test making a contour plot."""
@@ -431,7 +431,7 @@ def test_declarative_additional_layers_plot_options():
 
 @pytest.mark.mpl_image_compare(
     remove_text=True,
-    tolerance=2.74 if module_version_before('matplotlib', '3.8') else 1.91)
+    tolerance=2.74 if module_version_check('matplotlib<3.8') else 1.91)
 @needs_cartopy
 def test_declarative_contour_convert_units():
     """Test making a contour plot."""

tests/plots/test_skewt.py

@@ -11,7 +11,7 @@
 import pytest
 
 from metpy.plots import Hodograph, SkewT
-from metpy.testing import module_version_equal
+from metpy.testing import module_version_check
 from metpy.units import units
 
 
@@ -156,9 +156,9 @@ def test_skewt_units():
 
     # On Matplotlib <= 3.6, ax[hv]line() doesn't trigger unit labels
     assert skew.ax.get_xlabel() == (
-        'degree_Celsius' if module_version_equal('matplotlib', '3.7.0') else '')
+        'degree_Celsius' if module_version_check('matplotlib==3.7.0') else '')
     assert skew.ax.get_ylabel() == (
-        'hectopascal' if module_version_equal('matplotlib', '3.7.0') else '')
+        'hectopascal' if module_version_check('matplotlib==3.7.0') else '')
 
     # Clear them for the image test
     skew.ax.set_xlabel('')
@@ -321,7 +321,7 @@ def test_hodograph_api():
 
 
 @pytest.mark.mpl_image_compare(
-    remove_text=True, tolerance=0.6 if module_version_equal('matplotlib', '3.5') else 0.)
+    remove_text=True, tolerance=0.6 if module_version_check('matplotlib==3.5') else 0.)
 def test_hodograph_units():
     """Test passing quantities to Hodograph."""
     fig = plt.figure(figsize=(9, 9))

tests/plots/test_util.py

@@ -11,7 +11,7 @@
 import xarray as xr
 
 from metpy.plots import add_metpy_logo, add_timestamp, add_unidata_logo, convert_gempak_color
-from metpy.testing import get_test_data, module_version_before
+from metpy.testing import get_test_data, module_version_check
 
 
 @pytest.mark.mpl_image_compare(tolerance=2.638, remove_text=True)
@@ -92,7 +92,7 @@ def test_add_logo_invalid_size():
 
 
 @pytest.mark.mpl_image_compare(
-    tolerance=1.072 if module_version_before('matplotlib', '3.5') else 0,
+    tolerance=1.072 if module_version_check('matplotlib<3.5') else 0,
     remove_text=True)
 def test_gempak_color_image_compare():
     """Test creating a plot with all the GEMPAK colors."""
@@ -113,7 +113,7 @@ def test_gempak_color_image_compare():
 
 
 @pytest.mark.mpl_image_compare(
-    tolerance=1.215 if module_version_before('matplotlib', '3.5') else 0,
+    tolerance=1.215 if module_version_check('matplotlib<3.5') else 0,
     remove_text=True)
 def test_gempak_color_xw_image_compare():
     """Test creating a plot with all the GEMPAK colors using xw style."""

tests/test_testing.py

@@ -10,7 +10,7 @@
 
 from metpy.deprecation import MetpyDeprecationWarning
 from metpy.testing import (assert_array_almost_equal, check_and_drop_units,
-                           check_and_silence_deprecation)
+                           check_and_silence_deprecation, module_version_check)
 
 
 # Test #1183: numpy.testing.assert_array* ignores any masked value, so work-around
@@ -42,3 +42,22 @@ def test_check_and_drop_units_with_dataarray():
     assert isinstance(actual, np.ndarray)
     assert isinstance(desired, np.ndarray)
     np.testing.assert_array_almost_equal(actual, desired)
+
+
+def test_module_version_check():
+    """Test parsing and version comparison of installed package."""
+    assert module_version_check('numpy>0.0.0')
+    assert module_version_check('numpy >= 0.0')
+    assert module_version_check('numpy!=0')
+
+
+def test_module_version_check_nonsense():
+    """Test failed pattern match of package specification."""
+    with pytest.raises(ValueError, match='No valid version '):
+        module_version_check('thousands of birds picking packages')
+
+
+def test_module_version_check_invalid_comparison():
+    """Test invalid operator in version comparison."""
+    with pytest.raises(ValueError, match='Comparison operator not '):
+        module_version_check('numpy<<36')