Fix FacetGrid.set_titles #6839 (#6843)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: lopezvoliver

doc/whats-new.rst

@@ -42,6 +42,9 @@ Bug fixes
   By `Max Jones <https://github.com/maxrjones>`_.
 - Fix incompatibility with numpy 1.20 (:issue:`6818`, :pull:`6821`)
   By `Michael Niklas <https://github.com/headtr1ck>`_.
+- Make FacetGrid.set_titles send kwargs correctly using `handle.udpate(kwargs)`.
+  (:issue:`6839`, :pull:`6843`)
+  By `Oliver Lopez <https://github.com/lopezvoliver>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/plot/facetgrid.py

@@ -553,6 +553,7 @@ def set_titles(self, template="{coord} = {value}", maxchar=30, size=None, **kwar
                     )
                 else:
                     handle.set_text(title)
+                    handle.update(kwargs)
 
             # The column titles on the top row
             for index, (ax, col_name, handle) in enumerate(
@@ -563,6 +564,7 @@ def set_titles(self, template="{coord} = {value}", maxchar=30, size=None, **kwar
                     self.col_labels[index] = ax.set_title(title, size=size, **kwargs)
                 else:
                     handle.set_text(title)
+                    handle.update(kwargs)
 
         return self
 

xarray/tests/test_plot.py

@@ -112,6 +112,19 @@ def substring_not_in_axes(substring, ax):
     return all(check)
 
 
+def property_in_axes_text(property, property_str, target_txt, ax):
+    """
+    Return True if the specified text in an axes
+    has the property assigned to property_str
+    """
+    alltxt = ax.findobj(mpl.text.Text)
+    check = []
+    for t in alltxt:
+        if t.get_text() == target_txt:
+            check.append(plt.getp(t, property) == property_str)
+    return all(check)
+
+
 def easy_array(shape, start=0, stop=1):
     """
     Make an array with desired shape using np.linspace
@@ -2260,6 +2273,18 @@ def setUp(self):
 
         self.darray = darray
 
+    def test_title_kwargs(self):
+        g = xplt.FacetGrid(self.darray, col="col", row="row")
+        g.set_titles(template="{value}", weight="bold")
+
+        # Rightmost column titles should be bold
+        for label, ax in zip(self.darray.coords["row"].values, g.axes[:, -1]):
+            assert property_in_axes_text("weight", "bold", label, ax)
+
+        # Top row titles should be bold
+        for label, ax in zip(self.darray.coords["col"].values, g.axes[0, :]):
+            assert property_in_axes_text("weight", "bold", label, ax)
+
     @pytest.mark.slow
     def test_default_labels(self):
         g = xplt.FacetGrid(self.darray, col="col", row="row")