Add test.

Author: kschwab

tests/test_settings.py

@@ -662,6 +662,20 @@ def settings_customise_sources(
     assert s.model_dump() == s_final
 
 
+def test_alias_resolution_init_source(env):
+    class Example(BaseSettings):
+        model_config = SettingsConfigDict(env_prefix='PREFIX')
+
+        name: str
+        last_name: str = Field(validation_alias=AliasChoices('PREFIX_LAST_NAME', 'PREFIX_SURNAME'))
+
+    env.set('PREFIX_SURNAME', 'smith')
+    assert Example(name='john', PREFIX_SURNAME='doe').model_dump() == {
+        'name': 'john',
+        'last_name': 'doe'
+    }
+
+
 def test_alias_nested_model_default_partial_update():
     class SubModel(BaseModel):
         v1: str = 'default'