TST: Add test for front path effects

tests/plots/test_patheffects.py

@@ -0,0 +1,56 @@
+# Copyright (c) 2022 MetPy Developers.
+# Distributed under the terms of the BSD 3-Clause License.
+# SPDX-License-Identifier: BSD-3-Clause
+"""Test the `patheffects` module."""
+import matplotlib.pyplot as plt
+import numpy as np
+import pytest
+from scipy.interpolate import interp1d
+
+from metpy.plots import ColdFront, OccludedFront, StationaryFront, WarmFront
+
+
+@pytest.mark.mpl_image_compare(remove_text=True, tolerance=0.)
+def test_fronts():
+    """Basic test of plotting fronts using path effects."""
+    x = np.linspace(0, 80, 5)
+    fig, ax = plt.subplots(figsize=(12, 6), dpi=300)
+    ax.plot(x, x ** 3, linewidth=2, path_effects=[ColdFront(flip=True, spacing=1.0)])
+    ax.plot(x, 60000 * np.sqrt(x), linewidth=0.5,
+            path_effects=[WarmFront(spacing=1.0, color='brown')])
+    ax.plot(x, 75000 * np.sqrt(x), linewidth=1, path_effects=[OccludedFront(spacing=1.0)])
+    ax.plot(x, 6500 * x, linewidth=1, path_effects=[StationaryFront(spacing=1.0)])
+    return fig
+
+
+@pytest.mark.mpl_image_compare(remove_text=True, tolerance=0.)
+def test_curved_stationary():
+    """Test that curved stationary fronts don't have weird filled artifacts."""
+    n = 100
+    front_lat = [31.08, 31.76, 32.18, 32.01, 31.7, 32.44]
+    front_lon = [-88.08, -89.23, -90.83, -92.08, -93.27, -95.55]
+
+    index = np.arange(len(front_lon))
+    ii = np.linspace(0, index.max(), n)
+
+    xcurve = interp1d(index, front_lon, 'cubic')(ii)
+    ycurve = interp1d(index, front_lat, 'cubic')(ii)
+
+    fig, ax = plt.subplots()
+    ax.plot(xcurve, ycurve, path_effects=[StationaryFront(spacing=3, size=6)], linewidth=2)
+    return fig
+
+
+@pytest.mark.mpl_image_compare(remove_text=True, tolerance=0.)
+def test_stationary_spacing():
+    """Test various aspects of spacing around stationary fronts."""
+    x = [0, 1]
+    y = [1, 1]
+
+    fig, ax = plt.subplots()
+    ax.plot(x, y, path_effects=[StationaryFront(spacing=3, size=15)], linewidth=2)
+    ax.plot(x, [0.98, 0.98], path_effects=[StationaryFront(spacing=3, size=15)], linewidth=15)
+    ax.set_ylim(0.95, 1.05)
+    ax.set_xlim(-0.05, 1.05)
+
+    return fig