Add testing.check_figures_equal to avoid storing baseline images

pygmt/exceptions.py

@@ -44,3 +44,9 @@ class GMTVersionError(GMTError):
     """
     Raised when an incompatible version of GMT is being used.
     """
+
+
+class GMTImageComparisonFailure(AssertionError):
+    """
+    Raised when a comparison between two images fails.
+    """

pygmt/helpers/testing.py

@@ -0,0 +1,37 @@
+import os
+import sys
+from pathlib import Path
+
+from matplotlib.testing.compare import compare_images
+
+from ..exceptions import GMTImageComparisonFailure, GMTInvalidInput
+
+
+def check_figures_equal(fig_ref, fig_test, fig_prefix=None, tol=0.0):
+    result_dir = "result_images"
+
+    if not fig_prefix:
+        try:
+            fig_prefix = sys._getframe(1).f_code.co_name
+        except ValueError:
+            raise GMTInvalidInput("fig_prefix is required.")
+
+    os.makedirs(result_dir, exist_ok=True)
+
+    ref_image_path = os.path.join(result_dir, fig_prefix + "-expected.png")
+    test_image_path = os.path.join(result_dir, fig_prefix + ".png")
+
+    fig_ref.savefig(ref_image_path)
+    fig_test.savefig(test_image_path)
+
+    err = compare_images(ref_image_path, test_image_path, tol, in_decorator=True)
+
+    if err is None:  # Images are the same
+        os.remove(ref_image_path)
+        os.remove(test_image_path)
+    else:
+        for key in ["actual", "expected"]:
+            err[key] = os.path.relpath(err[key])
+        raise GMTImageComparisonFailure(
+            "images not close (RMS %(rms).3f):\n\t%(actual)s\n\t%(expected)s " % err
+        )

pygmt/tests/test.py

@@ -0,0 +1,9 @@
+from matplotlib.testing.decorators import check_figures_equal
+
+import pygmt
+
+
+@check_figures_equal(extensions=["png"])
+def test_plot(fig_test, fig_ref):
+    fig_test.subplots().plot([1, 3, 5])
+    fig_ref.subplots().plot([0, 1, 2], [1, 3, 5])

pygmt/tests/test_grdimage.py

@@ -8,6 +8,7 @@
 from .. import Figure
 from ..exceptions import GMTInvalidInput
 from ..datasets import load_earth_relief
+from ..helpers.testing import check_figures_equal
 
 
 @pytest.fixture(scope="module", name="grid")
@@ -93,3 +94,13 @@ def test_grdimage_over_dateline(xrgrid):
     xrgrid.gmt.gtype = 1  # geographic coordinate system
     fig.grdimage(grid=xrgrid, region="g", projection="A0/0/1c", V="i")
     return fig
+
+
+def test_grdimage_central_longitude(grid):
+    fig1 = Figure()
+    fig1.grdimage("@earth_relief_01d_g", projection="W120/15c", cmap="geo")
+
+    fig2 = Figure()
+    fig2.grdimage(grid, projection="W120/15c", cmap="geo")
+
+    check_figures_equal(fig1, fig2)

pygmt/tests/test_testing.py

@@ -0,0 +1,28 @@
+"""
+Test the testing functions for PyGMT
+"""
+import pytest
+
+from .. import Figure
+from ..exceptions import GMTImageComparisonFailure
+from ..helpers.testing import check_figures_equal
+
+
+def test_check_figures_equal():
+    fig_ref = Figure()
+    fig_ref.basemap(projection="X10c", region=[0, 10, 0, 10], frame=True)
+
+    fig_test = Figure()
+    fig_test.basemap(projection="X10c", region=[0, 10, 0, 10], frame=True)
+    check_figures_equal(fig_ref, fig_test)
+
+
+def test_check_figures_unequal():
+    fig_ref = Figure()
+    fig_ref.basemap(projection="X10c", region=[0, 10, 0, 10], frame=True)
+
+    fig_test = Figure()
+    fig_test.basemap(projection="X10c", region=[0, 15, 0, 15], frame=True)
+
+    with pytest.raises(GMTImageComparisonFailure):
+        check_figures_equal(fig_ref, fig_test)