tweak the fit of the parts

test/toolchain_test.rb

@@ -9,6 +9,7 @@ class ToolchainTest < Minitest::Test
 
     assert_match(/OpenSCAD/, error.message)
     assert_match(/Blender/, error.message)
+    assert_match(/Python 3/, error.message)
     assert_match(/apt-get/, error.message)
   end
 
@@ -18,13 +19,14 @@ class ToolchainTest < Minitest::Test
       File.write(executable, "#!/bin/sh\nexit 0\n")
       FileUtils.chmod(0o755, executable)
       toolchain = FeatherCaseWizard::Toolchain.new(
-        env: {"PATH" => "", "OPENSCAD" => executable, "BLENDER" => executable}
+        env: {"PATH" => "", "OPENSCAD" => executable, "BLENDER" => executable,
+              "PYTHON" => executable}
       )
 
       assert_equal executable, toolchain.openscad
       assert_equal executable, toolchain.blender
+      assert_equal executable, toolchain.python
       assert_same toolchain, toolchain.check!
     end
   end
 end
-