Ensure spaces in pygmt.config arguments can work

Also added a regression test for
FORMAT_DATE_MAP="o dd".

Author: weiji14

pygmt/src/config.py

@@ -55,7 +55,7 @@ def __init__(self, **kwargs):
                     self.old_defaults[key] = lib.get_default(key)
 
         # call gmt set to change GMT defaults
-        arg_str = " ".join([f"{key}={value}" for key, value in kwargs.items()])
+        arg_str = " ".join([f'{key}="{value}"' for key, value in kwargs.items()])
         with Session() as lib:
             lib.call_module("set", arg_str)
 

pygmt/tests/baseline/test_config_format_date_map.png.dvc

@@ -0,0 +1,4 @@
+outs:
+- md5: 3619720cdfcd857cbdbb49ed7fe6e930
+  size: 1392
+  path: test_config_format_date_map.png

pygmt/tests/test_config.py

@@ -64,6 +64,25 @@ def test_config_font_annot():
     return fig
 
 
+@pytest.mark.mpl_image_compare
+def test_config_format_date_map():
+    """
+    Test that setting FORMAT_DATE_MAP config changes how the output date string
+    is plotted.
+
+    Note the space in 'o dd', this acts as a regression test for
+    https://github.com/GenericMappingTools/pygmt/issues/247.
+    """
+    fig = Figure()
+    with config(FORMAT_DATE_MAP="o dd"):
+        fig.basemap(
+            region=["1969-7-21T", "1969-7-23T", 0, 1],
+            projection="X2.5c/0.1c",
+            frame=["sxa1D", "S"],
+        )
+    return fig
+
+
 @pytest.mark.mpl_image_compare
 def test_config_format_time_map():
     """