Note: this list is generated by looking for the string for this theme hook, so it may include some references that are not actually using this theme hook.

SystemThemeFunctionalTest::testAdministrationTheme in core/modules/system/tests/system.test
Test the administration theme functionality.
SystemThemeFunctionalTest::testPerThemeSettings in core/modules/system/tests/system.test
Test the individual per-theme settings form.
SystemThemeFunctionalTest::testThemeSettings in core/modules/system/tests/system.test
Test theme settings.
ThemeDebugMarkupTestCase::setUp in core/modules/simpletest/tests/theme.test
Sets up a Backdrop site for running functional and integration tests.
ThemeFastTestCase::setUp in core/modules/simpletest/tests/theme.test
Sets up a Backdrop site for running functional and integration tests.
ThemeHookInitUnitTest::setUp in core/modules/simpletest/tests/theme.test
Sets up a Backdrop site for running functional and integration tests.
ThemeHtmlTplPhpAttributesTestCase::setUp in core/modules/simpletest/tests/theme.test
Sets up a Backdrop site for running functional and integration tests.
ThemeRegistryTestCase::setUp in core/modules/simpletest/tests/theme.test
Sets up a Backdrop site for running functional and integration tests.
ThemeUnitTest::setUp in core/modules/simpletest/tests/theme.test
Sets up a Backdrop site for running functional and integration tests.
ThemeUnitTest::testRegistryRebuild in core/modules/simpletest/tests/theme.test
Ensures the theme registry is rebuilt when modules are disabled/enabled.
theme_test_system_theme_info in core/modules/simpletest/tests/theme_test.module
Implements hook_system_theme_info().
theme_test_theme in core/modules/simpletest/tests/theme_test.module
Implements hook_theme().
_theme_test_suggestion in core/modules/simpletest/tests/theme_test.module
Page callback, calls a theme hook suggestion.
_theme_test_suggestion in core/modules/simpletest/tests/theme_test.module
Page callback, calls a theme hook suggestion.