py-matplotlib: qualify when to do a post install (#44191)

* py-matplotlib: qualify when to do a post install

Older versions of py-matplotlib don't seem to have some of the
files that the post install step is trying to install.
Looks like the files first appeared in 3.6.0 and later.

Signed-off-by: Howard Pritchard <hppritcha@gmail.com>

* Change install paths for older matplotlib

---------

Signed-off-by: Howard Pritchard <hppritcha@gmail.com>
Co-authored-by: Adam J. Stewart <ajstewart426@gmail.com>

var/spack/repos/builtin/packages/py-matplotlib/package.py

@@ -331,16 +331,23 @@ def configure(self):
                     config.write("enable_lto = False\n")
 
     @run_after("install")
+    @on_package_attributes(run_tests=True)
     def copy_reference_images(self):
         # https://matplotlib.org/devdocs/devel/testing.html#obtain-the-reference-images
         install_tree(
             join_path("lib", "matplotlib", "tests", "baseline_images"),
             join_path(python_platlib, "matplotlib", "tests", "baseline_images"),
         )
-        for toolkit in ["axes_grid1", "axisartist", "mplot3d"]:
+        if self.spec.satisfies("@3.7:"):
+            for toolkit in ["axes_grid1", "axisartist", "mplot3d"]:
+                install_tree(
+                    join_path("lib", "mpl_toolkits", toolkit, "tests", "baseline_images"),
+                    join_path(python_platlib, "mpl_toolkits", toolkit, "tests", "baseline_images"),
+                )
+        else:
             install_tree(
-                join_path("lib", "mpl_toolkits", toolkit, "tests", "baseline_images"),
-                join_path(python_platlib, "mpl_toolkits", toolkit, "tests", "baseline_images"),
+                join_path("lib", "mpl_toolkits", "tests", "baseline_images"),
+                join_path(python_platlib, "mpl_toolkits", "tests", "baseline_images"),
             )
 
     @run_after("install")
@@ -348,5 +355,8 @@ def copy_reference_images(self):
     def install_test(self):
         # https://matplotlib.org/devdocs/devel/testing.html#run-the-tests
         python("-m", "pytest", "--pyargs", "matplotlib.tests")
-        for toolkit in ["axes_grid1", "axisartist", "mplot3d"]:
-            python("-m", "pytest", "--pyargs", f"mpl_toolkits.{toolkit}.tests")
+        if self.spec.satisfies("@3.7:"):
+            for toolkit in ["axes_grid1", "axisartist", "mplot3d"]:
+                python("-m", "pytest", "--pyargs", f"mpl_toolkits.{toolkit}.tests")
+        else:
+            python("-m", "pytest", "--pyargs", "mpl_toolkits.tests")