Ensure plotting xarray grids with different central meridians work on some projections

pygmt/helpers/testing.py

@@ -1,16 +1,16 @@
 """
 Helper functions for testing.
 """
-
 import inspect
 import os
+import string
 
 from matplotlib.testing.compare import compare_images
 
 from ..exceptions import GMTImageComparisonFailure
 
 
-def check_figures_equal(*, tol=0.0, result_dir="result_images"):
+def check_figures_equal(*, extensions=("png",), tol=0.0, result_dir="result_images"):
     """
     Decorator for test cases that generate and compare two figures.
 
@@ -25,6 +25,8 @@ def check_figures_equal(*, tol=0.0, result_dir="result_images"):
 
     Parameters
     ----------
+    extensions : list
+        The extensions to test. Default is ["png"].
     tol : float
         The RMS threshold above which the test is considered failed.
     result_dir : str
@@ -66,19 +68,30 @@ def check_figures_equal(*, tol=0.0, result_dir="result_images"):
     ...     )
     >>> shutil.rmtree(path="tmp_result_images")  # cleanup folder if tests pass
     """
+    # pylint: disable=invalid-name
+    ALLOWED_CHARS = set(string.digits + string.ascii_letters + "_-[]()")
+    KEYWORD_ONLY = inspect.Parameter.KEYWORD_ONLY
 
     def decorator(func):
+        import pytest
 
         os.makedirs(result_dir, exist_ok=True)
         old_sig = inspect.signature(func)
 
-        def wrapper(*args, **kwargs):
+        @pytest.mark.parametrize("ext", extensions)
+        def wrapper(*args, ext="png", request=None, **kwargs):
+            if "ext" in old_sig.parameters:
+                kwargs["ext"] = ext
+            if "request" in old_sig.parameters:
+                kwargs["request"] = request
+            try:
+                file_name = "".join(c for c in request.node.name if c in ALLOWED_CHARS)
+            except AttributeError:  # 'NoneType' object has no attribute 'node'
+                file_name = func.__name__
             try:
                 fig_ref, fig_test = func(*args, **kwargs)
-                ref_image_path = os.path.join(
-                    result_dir, func.__name__ + "-expected.png"
-                )
-                test_image_path = os.path.join(result_dir, func.__name__ + ".png")
+                ref_image_path = os.path.join(result_dir, f"{file_name}-expected.{ext}")
+                test_image_path = os.path.join(result_dir, f"{file_name}.{ext}")
                 fig_ref.savefig(ref_image_path)
                 fig_test.savefig(test_image_path)
 
@@ -109,9 +122,18 @@ def wrapper(*args, **kwargs):
             for param in old_sig.parameters.values()
             if param.name not in {"fig_test", "fig_ref"}
         ]
+        if "ext" not in old_sig.parameters:
+            parameters += [inspect.Parameter("ext", KEYWORD_ONLY)]
+        if "request" not in old_sig.parameters:
+            parameters += [inspect.Parameter("request", KEYWORD_ONLY)]
         new_sig = old_sig.replace(parameters=parameters)
         wrapper.__signature__ = new_sig
 
+        # reach a bit into pytest internals to hoist the marks from
+        # our wrapped function
+        new_marks = getattr(func, "pytestmark", []) + wrapper.pytestmark
+        wrapper.pytestmark = new_marks
+
         return wrapper
 
     return decorator

pygmt/tests/test_grdimage.py

@@ -114,12 +114,40 @@ def test_grdimage_over_dateline(xrgrid):
 
 
 @check_figures_equal()
-def test_grdimage_central_longitude(grid):
+@pytest.mark.parametrize("lon0", [0, 123, 180])
+@pytest.mark.parametrize("proj_type", ["H", "W"])
+def test_grdimage_central_meridians(grid, proj_type, lon0):
     """
-    Test that plotting a grid centred at different longitudes/meridians work.
+    Test that plotting a grid with different central meridians (lon0) using
+    Hammer (H) and Mollweide (W) projection systems work.
     """
     fig_ref = Figure()
-    fig_ref.grdimage("@earth_relief_01d_g", projection="W120/15c", cmap="geo")
+    fig_ref.grdimage(
+        "@earth_relief_01d_g", projection=f"{proj_type}{lon0}/15c", cmap="geo"
+    )
+    fig_test = Figure()
+    fig_test.grdimage(grid, projection=f"{proj_type}{lon0}/15c", cmap="geo")
+    return fig_ref, fig_test
+
+
+# Cylindrical Equidistant (Q) projections plotted with xarray and NetCDF grids
+# are still slightly different with an RMS error of 25, see issue at
+# https://github.com/GenericMappingTools/pygmt/issues/390
+# TO-DO remove tol=1.5 and pytest.mark.xfail once bug is solved in upstream GMT
+@check_figures_equal(tol=1.5)
+@pytest.mark.parametrize("lat0", [0, 30])
+@pytest.mark.parametrize("lon0", [0, 123, 180])
+@pytest.mark.parametrize("proj_type", [pytest.param("Q", marks=pytest.mark.xfail), "S"])
+def test_grdimage_central_meridians_and_standard_parallels(grid, proj_type, lon0, lat0):
+    """
+    Test that plotting a grid with different central meridians (lon0) and
+    standard_parallels (lat0) using Cylindrical Equidistant (Q) and General
+    Stereographic (S) projection systems work.
+    """
+    fig_ref = Figure()
+    fig_ref.grdimage(
+        "@earth_relief_01d_g", projection=f"{proj_type}{lon0}/{lat0}/15c", cmap="geo"
+    )
     fig_test = Figure()
-    fig_test.grdimage(grid, projection="W120/15c", cmap="geo")
+    fig_test.grdimage(grid, projection=f"{proj_type}{lon0}/{lat0}/15c", cmap="geo")
     return fig_ref, fig_test