Refactor test_logo tests to be simpler and more unit-test like

Author: weiji14

pygmt/tests/baseline/test_logo.png.dvc

@@ -1,4 +1,4 @@
 outs:
-- md5: 905d5b9f0f8d8b809899dfe9e87d0e91
-  size: 33347
+- md5: 61be9b262729e0a6b739e814d1aa4655
+  size: 32065
   path: test_logo.png

pygmt/tests/baseline/test_logo_on_a_map.png.dvc

@@ -1,4 +1,4 @@
 outs:
-- md5: 25854f87e4e6f4c30be71bc08a3d430c
-  size: 114522
+- md5: 57c3747cb7d2ed978e473d0f161ca3a6
+  size: 70993
   path: test_logo_on_a_map.png

pygmt/tests/test_logo.py

@@ -8,19 +8,19 @@
 @pytest.mark.mpl_image_compare
 def test_logo():
     """
-    Plot a GMT logo of a 2 inch width as a stand-alone plot.
+    Plot the GMT logo as a stand-alone plot.
     """
     fig = Figure()
-    fig.logo(position="x0/0+w2i")
+    fig.logo()
     return fig
 
 
 @pytest.mark.mpl_image_compare
 def test_logo_on_a_map():
     """
-    Plot a GMT logo in the upper right corner of a map.
+    Plot the GMT logo at the upper right corner of a map.
     """
     fig = Figure()
-    fig.coast(region=[-90, -70, 0, 20], projection="M6i", land="chocolate", frame=True)
-    fig.logo(position="jTR+o0.1i/0.1i+w3i", box=True)
+    fig.basemap(region=[-90, -70, 0, 20], projection="M15c", frame=True)
+    fig.logo(position="jTR+o0.25c/0.25c+w7.5c", box=True)
     return fig