consistently save/restore state when running tests

It's not obvious, but this is a refactoring. There should be no behavior
changes.

app.lua

@@ -428,22 +428,55 @@ function App.run_tests(record_error_fn)
     end
   end
   table.sort(sorted_names)
-  local saved_app = App
+  local globals = App.shallow_copy_all_globals()
   App = App_for_tests
+  local saved_font = love.graphics.getFont()
+  love.graphics.setFont(Love_snapshot.initial_font)
   for _,name in ipairs(sorted_names) do
     print(name)
     App.initialize_for_test()
     xpcall(_G[name], function(err) record_error_fn(name, err) end)
   end
-  App = saved_app
+  love.graphics.setFont(saved_font)
+  -- restore all global state except Test_errors
+  local test_errors = Test_errors
+  App.restore_all_globals(globals)
+  Test_errors = test_errors
 end
 
 function App.run_test(test, record_error_fn)
-  local saved_app = App
+  local globals = App.shallow_copy_all_globals()
   App = App_for_tests
-  App.initialize_for_test()
-  xpcall(test, function(err) record_error_fn('', err) end)
-  App = saved_app
+  local saved_font = love.graphics.getFont()
+  love.graphics.setFont(Love_snapshot.initial_font)
+    App.initialize_for_test()
+    xpcall(test, function(err) record_error_fn('', err) end)
+  love.graphics.setFont(saved_font)
+  -- restore all global state except Test_errors
+  local test_errors = Test_errors
+  App.restore_all_globals(globals)
+  Test_errors = test_errors
+end
+
+function App.shallow_copy_all_globals()
+  local result = {}
+  for k,v in pairs(_G) do
+    result[k] = v
+  end
+  return result
+end
+
+function App.restore_all_globals(x)
+  -- delete extra bindings
+  for k,v in pairs(_G) do
+    if x[k] == nil then
+      _G[k] = nil
+    end
+  end
+  -- restore previous bindings
+  for k,v in pairs(x) do
+    _G[k] = v
+  end
 end
 
 -- Test_errors will be an array

live.lua

@@ -279,35 +279,9 @@ function live.run(buf)
       return
     end
     -- run all tests
-    local globals = live.shallow_copy_all_globals()
-    local current_font = love.graphics.getFont()
-    love.graphics.setFont(Love_snapshot.initial_font)
     Test_errors = {}
     App.run_tests(record_error_by_test)
     live.send_to_driver(json.encode(Test_errors))
-    love.graphics.setFont(current_font)
-    live.restore_all_globals(globals)
-  end
-end
-
-function live.shallow_copy_all_globals()
-  local result = {}
-  for k,v in pairs(_G) do
-    result[k] = v
-  end
-  return result
-end
-
-function live.restore_all_globals(x)
-  -- delete extra bindings
-  for k,v in pairs(_G) do
-    if x[k] == nil then
-      _G[k] = nil
-    end
-  end
-  -- restore previous bindings
-  for k,v in pairs(x) do
-    _G[k] = v
   end
 end