[voice_assistant] Add unit tests for runtime model config handling

Covers the two Python behaviours a build YAML cannot: the conditional AUTO_LOAD
that keeps sha256 and json out of builds that do not download models, and the
validator rejecting http_request_id without micro_wake_word.

tests/unit_tests/components/voice_assistant/test_init.py

@@ -0,0 +1,44 @@
+"""Tests for the voice_assistant runtime model loading configuration."""
+
+import pytest
+
+from esphome.components import voice_assistant as va
+from esphome.components.http_request import CONF_HTTP_REQUEST_ID
+import esphome.config_validation as cv
+
+
+def test_auto_load_without_http_request_id() -> None:
+    """Devices that do not download models pull in nothing extra."""
+    assert va.AUTO_LOAD({}) == ["audio", "ring_buffer", "socket"]
+
+
+def test_auto_load_with_http_request_id() -> None:
+    """Downloading models needs sha256 to verify them and json to parse manifests."""
+    auto_load = va.AUTO_LOAD({CONF_HTTP_REQUEST_ID: "http_request_component"})
+    assert "sha256" in auto_load
+    assert "json" in auto_load
+
+
+def test_auto_load_with_no_config() -> None:
+    """AUTO_LOAD is also called with an empty config while the schema is being built."""
+    assert va.AUTO_LOAD(None) == ["audio", "ring_buffer", "socket"]
+
+
+def test_runtime_model_validate_requires_micro_wake_word() -> None:
+    """http_request_id is only useful alongside micro_wake_word, which runs the models."""
+    with pytest.raises(cv.Invalid, match=va.CONF_MICRO_WAKE_WORD):
+        va._runtime_model_validate({CONF_HTTP_REQUEST_ID: "http_request_component"})
+
+
+def test_runtime_model_validate_accepts_both() -> None:
+    config = {
+        CONF_HTTP_REQUEST_ID: "http_request_component",
+        va.CONF_MICRO_WAKE_WORD: "mww_component",
+    }
+    assert va._runtime_model_validate(config) is config
+
+
+def test_runtime_model_validate_accepts_neither() -> None:
+    """micro_wake_word alone stays valid; it just cannot download new models."""
+    config = {va.CONF_MICRO_WAKE_WORD: "mww_component"}
+    assert va._runtime_model_validate(config) is config