Fixed #17085, #24783 -- Refactored template library registration.

* Converted the ``libraries`` and ``builtins`` globals of
  ``django.template.base`` into properties of the Engine class.
* Added a public API for explicit registration of libraries and builtins.

35 files changed, 326 insertions, 79 deletions

diff --git a/tests/template_backends/apps/__init__.py b/tests/template_backends/apps/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/__init__.py
diff --git a/tests/template_backends/apps/good/__init__.py b/tests/template_backends/apps/good/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/good/__init__.py
diff --git a/tests/template_backends/apps/good/templatetags/__init__.py b/tests/template_backends/apps/good/templatetags/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/__init__.py
diff --git a/tests/template_backends/apps/good/templatetags/empty.py b/tests/template_backends/apps/good/templatetags/empty.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/empty.py
diff --git a/tests/template_backends/apps/good/templatetags/good_tags.py b/tests/template_backends/apps/good/templatetags/good_tags.py
new file mode 100644
index 0000000000..9bec93d8e5
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/good_tags.py
@@ -0,0 +1,3 @@
+from django.template import Library
+
+register = Library()
diff --git a/tests/template_backends/apps/good/templatetags/override.py b/tests/template_backends/apps/good/templatetags/override.py
new file mode 100644
index 0000000000..9bec93d8e5
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/override.py
@@ -0,0 +1,3 @@
+from django.template import Library
+
+register = Library()
diff --git a/tests/template_backends/apps/good/templatetags/subpackage/__init__.py b/tests/template_backends/apps/good/templatetags/subpackage/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/subpackage/__init__.py
diff --git a/tests/template_backends/apps/good/templatetags/subpackage/tags.py b/tests/template_backends/apps/good/templatetags/subpackage/tags.py
new file mode 100644
index 0000000000..9bec93d8e5
--- /dev/null
+++ b/tests/template_backends/apps/good/templatetags/subpackage/tags.py
@@ -0,0 +1,3 @@
+from django.template import Library
+
+register = Library()
diff --git a/tests/template_backends/apps/importerror/__init__.py b/tests/template_backends/apps/importerror/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/importerror/__init__.py
diff --git a/tests/template_backends/apps/importerror/templatetags/__init__.py b/tests/template_backends/apps/importerror/templatetags/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/tests/template_backends/apps/importerror/templatetags/__init__.py
diff --git a/tests/template_backends/apps/importerror/templatetags/broken_tags.py b/tests/template_backends/apps/importerror/templatetags/broken_tags.py
new file mode 100644
index 0000000000..4f240e5923
--- /dev/null
+++ b/tests/template_backends/apps/importerror/templatetags/broken_tags.py
@@ -0,0 +1 @@
+import DoesNotExist  # noqa
diff --git a/tests/template_backends/test_django.py b/tests/template_backends/test_django.py
index a8cc0d58b8..2a21b04b5a 100644
--- a/tests/template_backends/test_django.py
+++ b/tests/template_backends/test_django.py
@@ -2,7 +2,8 @@ from template_tests.test_response import test_processor_name
 
 from django.template import RequestContext
 from django.template.backends.django import DjangoTemplates
-from django.test import RequestFactory, ignore_warnings
+from django.template.library import InvalidTemplateLibrary
+from django.test import RequestFactory, ignore_warnings, override_settings
 from django.utils.deprecation import RemovedInDjango20Warning
 
 from .test_dummy import TemplateStringsTests
@@ -51,3 +52,78 @@ class DjangoTemplatesTests(TemplateStringsTests):
                "the two arguments refer to the same request.")
         with self.assertRaisesMessage(ValueError, msg):
             template.render(request_context, other_request)
+
+    @override_settings(INSTALLED_APPS=['template_backends.apps.good'])
+    def test_templatetag_discovery(self):
+        engine = DjangoTemplates({
+            'DIRS': [],
+            'APP_DIRS': False,
+            'NAME': 'django',
+            'OPTIONS': {
+                'libraries': {
+                    'alternate': 'template_backends.apps.good.templatetags.good_tags',
+                    'override': 'template_backends.apps.good.templatetags.good_tags',
+                },
+            },
+        })
+
+        # libraries are discovered from installed applications
+        self.assertEqual(
+            engine.engine.libraries['good_tags'],
+            'template_backends.apps.good.templatetags.good_tags',
+        )
+        self.assertEqual(
+            engine.engine.libraries['subpackage.tags'],
+            'template_backends.apps.good.templatetags.subpackage.tags',
+        )
+        # libraries are discovered from django.templatetags
+        self.assertEqual(
+            engine.engine.libraries['static'],
+            'django.templatetags.static',
+        )
+        # libraries passed in OPTIONS are registered
+        self.assertEqual(
+            engine.engine.libraries['alternate'],
+            'template_backends.apps.good.templatetags.good_tags',
+        )
+        # libraries passed in OPTIONS take precedence over discovered ones
+        self.assertEqual(
+            engine.engine.libraries['override'],
+            'template_backends.apps.good.templatetags.good_tags',
+        )
+
+    @override_settings(INSTALLED_APPS=['template_backends.apps.importerror'])
+    def test_templatetag_discovery_import_error(self):
+        """
+        Import errors in tag modules should be reraised with a helpful message.
+        """
+        with self.assertRaisesMessage(
+            InvalidTemplateLibrary,
+            "ImportError raised when trying to load "
+            "'template_backends.apps.importerror.templatetags.broken_tags'"
+        ):
+            DjangoTemplates({
+                'DIRS': [],
+                'APP_DIRS': False,
+                'NAME': 'django',
+                'OPTIONS': {},
+            })
+
+    def test_builtins_discovery(self):
+        engine = DjangoTemplates({
+            'DIRS': [],
+            'APP_DIRS': False,
+            'NAME': 'django',
+            'OPTIONS': {
+                'builtins': ['template_backends.apps.good.templatetags.good_tags'],
+            },
+        })
+
+        self.assertEqual(
+            engine.engine.builtins, [
+                'django.template.defaulttags',
+                'django.template.defaultfilters',
+                'django.template.loader_tags',
+                'template_backends.apps.good.templatetags.good_tags',
+            ]
+        )
diff --git a/tests/template_tests/templatetags/broken_tag.py b/tests/template_tests/broken_tag.py
index 414dc8412f..414dc8412f 100644
--- a/tests/template_tests/templatetags/broken_tag.py
+++ b/tests/template_tests/broken_tag.py
diff --git a/tests/template_tests/syntax_tests/test_cache.py b/tests/template_tests/syntax_tests/test_cache.py
index f088510d5d..2039e7808c 100644
--- a/tests/template_tests/syntax_tests/test_cache.py
+++ b/tests/template_tests/syntax_tests/test_cache.py
@@ -6,6 +6,10 @@ from ..utils import setup
 
 
 class CacheTagTests(SimpleTestCase):
+    libraries = {
+        'cache': 'django.templatetags.cache',
+        'custom': 'template_tests.templatetags.custom',
+    }
 
     def tearDown(self):
         cache.clear()
@@ -121,7 +125,7 @@ class CacheTests(SimpleTestCase):
 
     @classmethod
     def setUpClass(cls):
-        cls.engine = Engine()
+        cls.engine = Engine(libraries={'cache': 'django.templatetags.cache'})
         super(CacheTests, cls).setUpClass()
 
     def test_cache_regression_20130(self):
diff --git a/tests/template_tests/syntax_tests/test_cycle.py b/tests/template_tests/syntax_tests/test_cycle.py
index e2edf94c8d..c478faff52 100644
--- a/tests/template_tests/syntax_tests/test_cycle.py
+++ b/tests/template_tests/syntax_tests/test_cycle.py
@@ -6,6 +6,7 @@ from ..utils import setup
 
 
 class CycleTagTests(SimpleTestCase):
+    libraries = {'future': 'django.templatetags.future'}
 
     @setup({'cycle01': '{% cycle a %}'})
     def test_cycle01(self):
diff --git a/tests/template_tests/syntax_tests/test_extends.py b/tests/template_tests/syntax_tests/test_extends.py
index 1b0ff36a3c..3e65f4bf90 100644
--- a/tests/template_tests/syntax_tests/test_extends.py
+++ b/tests/template_tests/syntax_tests/test_extends.py
@@ -56,6 +56,7 @@ inheritance_templates = {
 
 
 class InheritanceTests(SimpleTestCase):
+    libraries = {'testtags': 'template_tests.templatetags.testtags'}
 
     @setup(inheritance_templates)
     def test_inheritance01(self):
diff --git a/tests/template_tests/syntax_tests/test_firstof.py b/tests/template_tests/syntax_tests/test_firstof.py
index a3c8c83151..79eb381c69 100644
--- a/tests/template_tests/syntax_tests/test_firstof.py
+++ b/tests/template_tests/syntax_tests/test_firstof.py
@@ -6,6 +6,7 @@ from ..utils import setup
 
 
 class FirstOfTagTests(SimpleTestCase):
+    libraries = {'future': 'django.templatetags.future'}
 
     @setup({'firstof01': '{% firstof a b c %}'})
     def test_firstof01(self):
diff --git a/tests/template_tests/syntax_tests/test_for.py b/tests/template_tests/syntax_tests/test_for.py
index 566b86f3d8..8045ea4990 100644
--- a/tests/template_tests/syntax_tests/test_for.py
+++ b/tests/template_tests/syntax_tests/test_for.py
@@ -6,6 +6,7 @@ from ..utils import setup
 
 
 class ForTagTests(SimpleTestCase):
+    libraries = {'custom': 'template_tests.templatetags.custom'}
 
     @setup({'for-tag01': '{% for val in values %}{{ val }}{% endfor %}'})
     def test_for_tag01(self):
diff --git a/tests/template_tests/syntax_tests/test_i18n.py b/tests/template_tests/syntax_tests/test_i18n.py
index da53a8c279..1d0f83478a 100644
--- a/tests/template_tests/syntax_tests/test_i18n.py
+++ b/tests/template_tests/syntax_tests/test_i18n.py
@@ -10,6 +10,10 @@ from ..utils import setup
 
 
 class I18nTagTests(SimpleTestCase):
+    libraries = {
+        'custom': 'template_tests.templatetags.custom',
+        'i18n': 'django.templatetags.i18n',
+    }
 
     @setup({'i18n01': '{% load i18n %}{% trans \'xxxyyyxxx\' %}'})
     def test_i18n01(self):
diff --git a/tests/template_tests/syntax_tests/test_if_changed.py b/tests/template_tests/syntax_tests/test_if_changed.py
index 62f9563020..09cdc34a88 100644
--- a/tests/template_tests/syntax_tests/test_if_changed.py
+++ b/tests/template_tests/syntax_tests/test_if_changed.py
@@ -5,6 +5,7 @@ from ..utils import setup
 
 
 class IfChangedTagTests(SimpleTestCase):
+    libraries = {'custom': 'template_tests.templatetags.custom'}
 
     @setup({'ifchanged01': '{% for n in num %}{% ifchanged %}{{ n }}{% endifchanged %}{% endfor %}'})
     def test_ifchanged01(self):
diff --git a/tests/template_tests/syntax_tests/test_include.py b/tests/template_tests/syntax_tests/test_include.py
index 5a05b32c33..fc1554a17e 100644
--- a/tests/template_tests/syntax_tests/test_include.py
+++ b/tests/template_tests/syntax_tests/test_include.py
@@ -13,6 +13,7 @@ include_fail_templates = {
 
 
 class IncludeTagTests(SimpleTestCase):
+    libraries = {'bad_tag': 'template_tests.templatetags.bad_tag'}
 
     @setup({'include01': '{% include "basic-syntax01" %}'}, basic_templates)
     def test_include01(self):
diff --git a/tests/template_tests/syntax_tests/test_invalid_string.py b/tests/template_tests/syntax_tests/test_invalid_string.py
index 2bb8c71fd1..18520aa7bf 100644
--- a/tests/template_tests/syntax_tests/test_invalid_string.py
+++ b/tests/template_tests/syntax_tests/test_invalid_string.py
@@ -4,6 +4,7 @@ from ..utils import setup
 
 
 class InvalidStringTests(SimpleTestCase):
+    libraries = {'i18n': 'django.templatetags.i18n'}
 
     @setup({'invalidstr01': '{{ var|default:"Foo" }}'})
     def test_invalidstr01(self):
diff --git a/tests/template_tests/syntax_tests/test_load.py b/tests/template_tests/syntax_tests/test_load.py
index 711a9da632..919bbf1346 100644
--- a/tests/template_tests/syntax_tests/test_load.py
+++ b/tests/template_tests/syntax_tests/test_load.py
@@ -5,6 +5,10 @@ from ..utils import setup
 
 
 class LoadTagTests(SimpleTestCase):
+    libraries = {
+        'subpackage.echo': 'template_tests.templatetags.subpackage.echo',
+        'testtags': 'template_tests.templatetags.testtags',
+    }
 
     @setup({'load01': '{% load testtags subpackage.echo %}{% echo test %} {% echo2 "test" %}'})
     def test_load01(self):
@@ -42,30 +46,30 @@ class LoadTagTests(SimpleTestCase):
     # {% load %} tag errors
     @setup({'load07': '{% load echo other_echo bad_tag from testtags %}'})
     def test_load07(self):
-        with self.assertRaises(TemplateSyntaxError):
+        msg = "'bad_tag' is not a valid tag or filter in tag library 'testtags'"
+        with self.assertRaisesMessage(TemplateSyntaxError, msg):
             self.engine.get_template('load07')
 
     @setup({'load08': '{% load echo other_echo bad_tag from %}'})
     def test_load08(self):
-        with self.assertRaises(TemplateSyntaxError):
+        msg = "'echo' is not a registered tag library. Must be one of:\nsubpackage.echo\ntesttags"
+        with self.assertRaisesMessage(TemplateSyntaxError, msg):
             self.engine.get_template('load08')
 
     @setup({'load09': '{% load from testtags %}'})
     def test_load09(self):
-        with self.assertRaises(TemplateSyntaxError):
+        msg = "'from' is not a registered tag library. Must be one of:\nsubpackage.echo\ntesttags"
+        with self.assertRaisesMessage(TemplateSyntaxError, msg):
             self.engine.get_template('load09')
 
     @setup({'load10': '{% load echo from bad_library %}'})
     def test_load10(self):
-        with self.assertRaises(TemplateSyntaxError):
+        msg = "'bad_library' is not a registered tag library. Must be one of:\nsubpackage.echo\ntesttags"
+        with self.assertRaisesMessage(TemplateSyntaxError, msg):
             self.engine.get_template('load10')
 
-    @setup({'load11': '{% load subpackage.echo_invalid %}'})
-    def test_load11(self):
-        with self.assertRaises(TemplateSyntaxError):
-            self.engine.get_template('load11')
-
     @setup({'load12': '{% load subpackage.missing %}'})
     def test_load12(self):
-        with self.assertRaises(TemplateSyntaxError):
+        msg = "'subpackage.missing' is not a registered tag library. Must be one of:\nsubpackage.echo\ntesttags"
+        with self.assertRaisesMessage(TemplateSyntaxError, msg):
             self.engine.get_template('load12')
diff --git a/tests/template_tests/syntax_tests/test_simple_tag.py b/tests/template_tests/syntax_tests/test_simple_tag.py
index b89af4c72b..5e6ce4733e 100644
--- a/tests/template_tests/syntax_tests/test_simple_tag.py
+++ b/tests/template_tests/syntax_tests/test_simple_tag.py
@@ -5,6 +5,7 @@ from ..utils import setup
 
 
 class SimpleTagTests(SimpleTestCase):
+    libraries = {'custom': 'template_tests.templatetags.custom'}
 
     @setup({'simpletag-renamed01': '{% load custom %}{% minusone 7 %}'})
     def test_simpletag_renamed01(self):
diff --git a/tests/template_tests/syntax_tests/test_static.py b/tests/template_tests/syntax_tests/test_static.py
index b646ac2bb8..8ff90f5a5c 100644
--- a/tests/template_tests/syntax_tests/test_static.py
+++ b/tests/template_tests/syntax_tests/test_static.py
@@ -7,6 +7,7 @@ from ..utils import setup
 
 @override_settings(MEDIA_URL="/media/", STATIC_URL="/static/")
 class StaticTagTests(SimpleTestCase):
+    libraries = {'static': 'django.templatetags.static'}
 
     @setup({'static-prefixtag01': '{% load static %}{% get_static_prefix %}'})
     def test_static_prefixtag01(self):
diff --git a/tests/template_tests/syntax_tests/test_width_ratio.py b/tests/template_tests/syntax_tests/test_width_ratio.py
index 9799b7d6ab..8206b83c58 100644
--- a/tests/template_tests/syntax_tests/test_width_ratio.py
+++ b/tests/template_tests/syntax_tests/test_width_ratio.py
@@ -6,6 +6,7 @@ from ..utils import setup
 
 
 class WidthRatioTagTests(SimpleTestCase):
+    libraries = {'custom': 'template_tests.templatetags.custom'}
 
     @setup({'widthratio01': '{% widthratio a b 0 %}'})
     def test_widthratio01(self):
diff --git a/tests/template_tests/templatetags/subpackage/echo_invalid.py b/tests/template_tests/templatetags/subpackage/echo_invalid.py
deleted file mode 100644
index 0764b9c8fa..0000000000
--- a/tests/template_tests/templatetags/subpackage/echo_invalid.py
+++ /dev/null
@@ -1 +0,0 @@
-import nonexistent.module  # NOQA
diff --git a/tests/template_tests/templatetags/testtags.py b/tests/template_tests/templatetags/testtags.py
new file mode 100644
index 0000000000..41b65a2ed1
--- /dev/null
+++ b/tests/template_tests/templatetags/testtags.py
@@ -0,0 +1,22 @@
+from django.template import Library, Node
+
+register = Library()
+
+
+class EchoNode(Node):
+    def __init__(self, contents):
+        self.contents = contents
+
+    def render(self, context):
+        return ' '.join(self.contents)
+
+
+@register.tag
+def echo(parser, token):
+    return EchoNode(token.contents.split()[1:])
+register.tag('other_echo', echo)
+
+
+@register.filter
+def upper(value):
+    return value.upper()
diff --git a/tests/template_tests/test_custom.py b/tests/template_tests/test_custom.py
index b5c125c61c..11c04f870c 100644
--- a/tests/template_tests/test_custom.py
+++ b/tests/template_tests/test_custom.py
@@ -4,18 +4,26 @@ import os
 
 from django.template import Context, Engine, TemplateSyntaxError
 from django.template.base import Node
+from django.template.library import InvalidTemplateLibrary
 from django.test import SimpleTestCase, ignore_warnings
 from django.test.utils import extend_sys_path
+from django.utils import six
 from django.utils.deprecation import RemovedInDjango20Warning
 
 from .templatetags import custom, inclusion
 from .utils import ROOT
 
+LIBRARIES = {
+    'custom': 'template_tests.templatetags.custom',
+    'inclusion': 'template_tests.templatetags.inclusion',
+}
+
 
 class CustomFilterTests(SimpleTestCase):
 
     def test_filter(self):
-        t = Engine().from_string("{% load custom %}{{ string|trim:5 }}")
+        engine = Engine(libraries=LIBRARIES)
+        t = engine.from_string("{% load custom %}{{ string|trim:5 }}")
         self.assertEqual(
             t.render(Context({"string": "abcdefghijklmnopqrstuvwxyz"})),
             "abcde"
@@ -26,7 +34,7 @@ class TagTestCase(SimpleTestCase):
 
     @classmethod
     def setUpClass(cls):
-        cls.engine = Engine(app_dirs=True)
+        cls.engine = Engine(app_dirs=True, libraries=LIBRARIES)
         super(TagTestCase, cls).setUpClass()
 
     def verify_tag(self, tag, name):
@@ -269,7 +277,7 @@ class InclusionTagTests(TagTestCase):
         """
         #23441 -- InclusionNode shouldn't modify its nodelist at render time.
         """
-        engine = Engine(app_dirs=True)
+        engine = Engine(app_dirs=True, libraries=LIBRARIES)
         template = engine.from_string('{% load inclusion %}{% inclusion_no_params %}')
         count = template.nodelist.get_nodes_by_type(Node)
         template.render(Context({}))
@@ -281,7 +289,7 @@ class InclusionTagTests(TagTestCase):
         when rendering. Otherwise, leftover values such as blocks from
         extending can interfere with subsequent rendering.
         """
-        engine = Engine(app_dirs=True)
+        engine = Engine(app_dirs=True, libraries=LIBRARIES)
         template = engine.from_string('{% load inclusion %}{% inclusion_extends1 %}{% inclusion_extends2 %}')
         self.assertEqual(template.render(Context({})).strip(), 'one\ntwo')
 
@@ -313,34 +321,37 @@ class TemplateTagLoadingTests(SimpleTestCase):
     @classmethod
     def setUpClass(cls):
         cls.egg_dir = os.path.join(ROOT, 'eggs')
-        cls.engine = Engine()
         super(TemplateTagLoadingTests, cls).setUpClass()
 
     def test_load_error(self):
-        ttext = "{% load broken_tag %}"
-        with self.assertRaises(TemplateSyntaxError) as e:
-            self.engine.from_string(ttext)
-
-        self.assertIn('ImportError', e.exception.args[0])
-        self.assertIn('Xtemplate', e.exception.args[0])
+        msg = (
+            "Invalid template library specified. ImportError raised when "
+            "trying to load 'template_tests.broken_tag': cannot import name "
+            "'?Xtemplate'?"
+        )
+        with six.assertRaisesRegex(self, InvalidTemplateLibrary, msg):
+            Engine(libraries={
+                'broken_tag': 'template_tests.broken_tag',
+            })
 
     def test_load_error_egg(self):
-        ttext = "{% load broken_egg %}"
         egg_name = '%s/tagsegg.egg' % self.egg_dir
+        msg = (
+            "Invalid template library specified. ImportError raised when "
+            "trying to load 'tagsegg.templatetags.broken_egg': cannot "
+            "import name '?Xtemplate'?"
+        )
         with extend_sys_path(egg_name):
-            with self.assertRaises(TemplateSyntaxError):
-                with self.settings(INSTALLED_APPS=['tagsegg']):
-                    self.engine.from_string(ttext)
-            try:
-                with self.settings(INSTALLED_APPS=['tagsegg']):
-                    self.engine.from_string(ttext)
-            except TemplateSyntaxError as e:
-                self.assertIn('ImportError', e.args[0])
-                self.assertIn('Xtemplate', e.args[0])
+            with six.assertRaisesRegex(self, InvalidTemplateLibrary, msg):
+                Engine(libraries={
+                    'broken_egg': 'tagsegg.templatetags.broken_egg',
+                })
 
     def test_load_working_egg(self):
         ttext = "{% load working_egg %}"
         egg_name = '%s/tagsegg.egg' % self.egg_dir
         with extend_sys_path(egg_name):
-            with self.settings(INSTALLED_APPS=['tagsegg']):
-                self.engine.from_string(ttext)
+            engine = Engine(libraries={
+                'working_egg': 'tagsegg.templatetags.working_egg',
+            })
+            engine.from_string(ttext)
diff --git a/tests/template_tests/test_engine.py b/tests/template_tests/test_engine.py
index d9929660cc..a72a430e3e 100644
--- a/tests/template_tests/test_engine.py
+++ b/tests/template_tests/test_engine.py
@@ -14,7 +14,10 @@ OTHER_DIR = os.path.join(ROOT, 'other_templates')
 class DeprecatedRenderToStringTest(SimpleTestCase):
 
     def setUp(self):
-        self.engine = Engine(dirs=[TEMPLATE_DIR])
+        self.engine = Engine(
+            dirs=[TEMPLATE_DIR],
+            libraries={'custom': 'template_tests.templatetags.custom'},
+        )
 
     def test_basic_context(self):
         self.assertEqual(
diff --git a/tests/template_tests/test_library.py b/tests/template_tests/test_library.py
new file mode 100644
index 0000000000..50a00ca082
--- /dev/null
+++ b/tests/template_tests/test_library.py
@@ -0,0 +1,132 @@
+from django.template import Library
+from django.template.base import Node
+from django.test import TestCase
+
+
+class FilterRegistrationTests(TestCase):
+
+    def setUp(self):
+        self.library = Library()
+
+    def test_filter(self):
+        @self.library.filter
+        def func():
+            return ''
+        self.assertEqual(self.library.filters['func'], func)
+
+    def test_filter_parens(self):
+        @self.library.filter()
+        def func():
+            return ''
+        self.assertEqual(self.library.filters['func'], func)
+
+    def test_filter_name_arg(self):
+        @self.library.filter('name')
+        def func():
+            return ''
+        self.assertEqual(self.library.filters['name'], func)
+
+    def test_filter_name_kwarg(self):
+        @self.library.filter(name='name')
+        def func():
+            return ''
+        self.assertEqual(self.library.filters['name'], func)
+
+    def test_filter_call(self):
+        def func():
+            return ''
+        self.library.filter('name', func)
+        self.assertEqual(self.library.filters['name'], func)
+
+    def test_filter_invalid(self):
+        msg = "Unsupported arguments to Library.filter: (None, '')"
+        with self.assertRaisesMessage(ValueError, msg):
+            self.library.filter(None, '')
+
+
+class InclusionTagRegistrationTests(TestCase):
+
+    def setUp(self):
+        self.library = Library()
+
+    def test_inclusion_tag(self):
+        @self.library.inclusion_tag('template.html')
+        def func():
+            return ''
+        self.assertIn('func', self.library.tags)
+
+    def test_inclusion_tag_name(self):
+        @self.library.inclusion_tag('template.html', name='name')
+        def func():
+            return ''
+        self.assertIn('name', self.library.tags)
+
+
+class SimpleTagRegistrationTests(TestCase):
+
+    def setUp(self):
+        self.library = Library()
+
+    def test_simple_tag(self):
+        @self.library.simple_tag
+        def func():
+            return ''
+        self.assertIn('func', self.library.tags)
+
+    def test_simple_tag_parens(self):
+        @self.library.simple_tag()
+        def func():
+            return ''
+        self.assertIn('func', self.library.tags)
+
+    def test_simple_tag_name_kwarg(self):
+        @self.library.simple_tag(name='name')
+        def func():
+            return ''
+        self.assertIn('name', self.library.tags)
+
+    def test_simple_tag_invalid(self):
+        msg = "Invalid arguments provided to simple_tag"
+        with self.assertRaisesMessage(ValueError, msg):
+            self.library.simple_tag('invalid')
+
+
+class TagRegistrationTests(TestCase):
+
+    def setUp(self):
+        self.library = Library()
+
+    def test_tag(self):
+        @self.library.tag
+        def func(parser, token):
+            return Node()
+        self.assertEqual(self.library.tags['func'], func)
+
+    def test_tag_parens(self):
+        @self.library.tag()
+        def func(parser, token):
+            return Node()
+        self.assertEqual(self.library.tags['func'], func)
+
+    def test_tag_name_arg(self):
+        @self.library.tag('name')
+        def func(parser, token):
+            return Node()
+        self.assertEqual(self.library.tags['name'], func)
+
+    def test_tag_name_kwarg(self):
+        @self.library.tag(name='name')
+        def func(parser, token):
+            return Node()
+        self.assertEqual(self.library.tags['name'], func)
+
+    def test_tag_call(self):
+        def func(parser, token):
+            return Node()
+        self.library.tag('name', func)
+        self.assertEqual(self.library.tags['name'], func)
+
+    def test_tag_invalid(self):
+        msg = "Unsupported arguments to Library.tag: (None, '')"
+        with self.assertRaisesMessage(ValueError, msg):
+            self.library.tag(None, '')
diff --git a/tests/template_tests/test_nodelist.py b/tests/template_tests/test_nodelist.py
index 3f28aff92c..3070c9d68a 100644
--- a/tests/template_tests/test_nodelist.py
+++ b/tests/template_tests/test_nodelist.py
@@ -49,7 +49,7 @@ class ErrorIndexTest(TestCase):
             'range': range(5),
             'five': 5,
         })
-        engine = Engine(debug=True)
+        engine = Engine(debug=True, libraries={'bad_tag': 'template_tests.templatetags.bad_tag'})
         for source, expected_error_source_index in tests:
             template = engine.from_string(source)
             try:
diff --git a/tests/template_tests/test_parser.py b/tests/template_tests/test_parser.py
index dd22c83836..6ff57c2cf5 100644
--- a/tests/template_tests/test_parser.py
+++ b/tests/template_tests/test_parser.py
@@ -9,6 +9,7 @@ from django.template import Library, TemplateSyntaxError
 from django.template.base import (
     TOKEN_BLOCK, FilterExpression, Parser, Token, Variable,
 )
+from django.template.defaultfilters import register as filter_library
 from django.utils import six
 
 
@@ -24,7 +25,7 @@ class ParserTests(TestCase):
 
     def test_filter_parsing(self):
         c = {"article": {"section": "News"}}
-        p = Parser("")
+        p = Parser("", builtins=[filter_library])
 
         def fe_test(s, val):
             self.assertEqual(FilterExpression(s, p).resolve(c), val)
diff --git a/tests/template_tests/tests.py b/tests/template_tests/tests.py
index 436502305e..39f0b427d6 100644
--- a/tests/template_tests/tests.py
+++ b/tests/template_tests/tests.py
@@ -97,7 +97,10 @@ class TemplateTests(SimpleTestCase):
         Errors raised while compiling nodes should include the token
         information.
         """
-        engine = Engine(debug=True)
+        engine = Engine(
+            debug=True,
+            libraries={'bad_tag': 'template_tests.templatetags.bad_tag'},
+        )
         with self.assertRaises(RuntimeError) as e:
             engine.from_string("{% load bad_tag %}{% badtag %}")
         self.assertEqual(e.exception.template_debug['during'], '{% badtag %}')
diff --git a/tests/template_tests/utils.py b/tests/template_tests/utils.py
index 36f4d95678..d78f0eac6c 100644
--- a/tests/template_tests/utils.py
+++ b/tests/template_tests/utils.py
@@ -5,9 +5,6 @@ from __future__ import unicode_literals
 import functools
 import os
 
-from django import template
-from django.template import Library
-from django.template.base import libraries
 from django.template.engine import Engine
 from django.test.utils import override_settings
 from django.utils._os import upath
@@ -49,14 +46,17 @@ def setup(templates, *args, **kwargs):
     ]
 
     def decorator(func):
-        @register_test_tags
         # Make Engine.get_default() raise an exception to ensure that tests
         # are properly isolated from Django's global settings.
         @override_settings(TEMPLATES=None)
         @functools.wraps(func)
         def inner(self):
+            # Set up custom template tag libraries if specified
+            libraries = getattr(self, 'libraries', {})
+
             self.engine = Engine(
                 allowed_include_roots=[ROOT],
+                libraries=libraries,
                 loaders=loaders,
             )
             func(self)
@@ -66,6 +66,7 @@ def setup(templates, *args, **kwargs):
 
             self.engine = Engine(
                 allowed_include_roots=[ROOT],
+                libraries=libraries,
                 loaders=loaders,
                 string_if_invalid='INVALID',
             )
@@ -75,6 +76,7 @@ def setup(templates, *args, **kwargs):
             self.engine = Engine(
                 allowed_include_roots=[ROOT],
                 debug=True,
+                libraries=libraries,
                 loaders=loaders,
             )
             func(self)
@@ -85,43 +87,9 @@ def setup(templates, *args, **kwargs):
     return decorator
 
 
-# Custom template tag for tests
-
-register = Library()
-
-
-class EchoNode(template.Node):
-    def __init__(self, contents):
-        self.contents = contents
-
-    def render(self, context):
-        return ' '.join(self.contents)
-
-
-@register.tag
-def echo(parser, token):
-    return EchoNode(token.contents.split()[1:])
-register.tag('other_echo', echo)
-
-
-@register.filter
-def upper(value):
-    return value.upper()
-
-
-def register_test_tags(func):
-    @functools.wraps(func)
-    def inner(self):
-        libraries['testtags'] = register
-        try:
-            func(self)
-        finally:
-            del libraries['testtags']
-    return inner
-
-
 # Helper objects
 
+
 class SomeException(Exception):
     silent_variable_failure = True