tests: Add smoke test for extra context feature

Test custom extra context registration with @extra_context decorator,
load() function in templates, and Template.extra field.

Co-Authored-By: MiMo v2 Pro <mimo@xiaomi.com>

Author: SilverRainZ

tests/roots/test-extra-context/conf.py

@@ -0,0 +1,41 @@
+from sphinx.application import Sphinx
+from sphinxnotes.render import (
+    extra_context,
+    ParsingPhaseExtraContext,
+    GlobalExtraContext,
+    BaseContextDirective,
+    Template,
+)
+
+
+@extra_context('custom_parsing')
+class CustomParsingExtraContext(ParsingPhaseExtraContext):
+    def generate(self, directive):
+        return {'custom_value': 'parsing_test'}
+
+
+@extra_context('custom_global')
+class CustomGlobalExtraContext(GlobalExtraContext):
+    def generate(self, env):
+        return {'custom_value': 'global_test'}
+
+
+class CustomExtraContextDirective(BaseContextDirective):
+    def current_context(self):
+        return {}
+
+    def current_template(self):
+        return Template(
+            """
+{% set _parsing = load('custom_parsing') %}
+{% set _global = load('custom_global') %}
+Parsing: {{ _parsing.custom_value }}
+Global: {{ _global.custom_value }}
+""",
+            extra=['custom_parsing', 'custom_global'],
+        )
+
+
+def setup(app: Sphinx):
+    app.setup_extension('sphinxnotes.render')
+    app.add_directive('custom-extra', CustomExtraContextDirective)

tests/roots/test-extra-context/index.rst

@@ -0,0 +1,4 @@
+Extra Context Test
+==================
+
+.. custom-extra::

tests/test_smoke.py

@@ -26,3 +26,13 @@ def test_strict_data_define_directive_card(app, status, warning):
 
 
 # -- literalinclude:end:end-to-end-card --
+
+
+@pytest.mark.sphinx('html', testroot='extra-context')
+def test_extra_context_custom_loader(app, status, warning):
+    app.build()
+
+    html = (app.outdir / 'index.html').read_text(encoding='utf-8')
+
+    assert 'Parsing: parsing_test' in html
+    assert 'Global: global_test' in html