Use pytest.importorskip for sphinx_gallery test (#1525)

Completes code coverage of the sphinx_gallery.py
file which had the `except ImportError: figure_rst = None`
lines not covered by Continuous Integration tests.

Author: weiji14

pygmt/sphinx_gallery.py

@@ -1,11 +1,8 @@
 """
 Utilities for using pygmt with sphinx-gallery.
 """
-try:
-    from sphinx_gallery.scrapers import figure_rst
-except ImportError:
-    figure_rst = None
 
+import sphinx_gallery.scrapers
 from pygmt.figure import SHOWED_FIGURES
 
 
@@ -32,4 +29,4 @@ def __call__(self, block, block_vars, gallery_conf):
             fig = figures.pop(0)
             fig.savefig(fname, transparent=True, dpi=200)
             image_names.append(fname)
-        return figure_rst(image_names, gallery_conf["src_dir"])
+        return sphinx_gallery.scrapers.figure_rst(image_names, gallery_conf["src_dir"])

pygmt/tests/test_sphinx_gallery.py

@@ -5,17 +5,13 @@
 from tempfile import TemporaryDirectory
 
 import pytest
-
-try:
-    import sphinx_gallery
-except ImportError:
-    sphinx_gallery = None
-
 from pygmt.figure import SHOWED_FIGURES, Figure
-from pygmt.sphinx_gallery import PyGMTScraper
+
+pygmt_sphinx_gallery = pytest.importorskip(
+    "pygmt.sphinx_gallery", reason="requires sphinx-gallery to be installed"
+)
 
 
-@pytest.mark.skipif(sphinx_gallery is None, reason="requires sphinx-gallery")
 def test_pygmtscraper():
     """
     Make sure the scraper finds the figures and removes them from the pool.
@@ -30,7 +26,7 @@ def test_pygmtscraper():
         fig.show()
         assert len(SHOWED_FIGURES) == 1
         assert SHOWED_FIGURES[0] is fig
-        scraper = PyGMTScraper()
+        scraper = pygmt_sphinx_gallery.PyGMTScraper()
         with TemporaryDirectory(dir=os.getcwd()) as tmpdir:
             conf = {"src_dir": "meh"}
             fname = os.path.join(tmpdir, "meh.png")