add test for case where language cannot be detected

.pre-commit-config.yaml

@@ -51,7 +51,7 @@ repos:
         args:
           [
             "-L",
-            "newyorker,te,responde,ist,als,oder,technik,sie,rouge,unter,juli,fiel,couldn,mke, vor",
+            "newyorker,te,responde,ist,als,oder,technik,sie,rouge,unter,juli,fiel,couldn,mke, vor,fille,ans",
           ]
         exclude: '^(poetry\.lock|trace-viewer/.*|tests/connectors/retrievers/test_document_index_retriever\.py|src/intelligence_layer/use_cases/qa/multiple_chunk_qa.py|src/intelligence_layer/use_cases/summarize/.*|tests/connectors/retrievers/test_document_index_retriever\.py|src/intelligence_layer/use_cases/classify/keyword_extract.py|tests/use_cases/summarize/test_single_chunk_few_shot_summarize.py|tests/use_cases/summarize/very_long_text.txt)$'
   - repo: https://github.com/akaihola/darglint2

tests/core/test_detect_language.py

@@ -17,3 +17,16 @@ def test_detect_language_returns_correct_language() -> None:
     output = task.run(input, tracer)
 
     assert output.best_fit == Language("en")
+
+
+def test_detect_language_returns_non_if_no_language_can_be_detected() -> None:
+    text = "Je m’appelle Jessica. Je suis une fille, je suis française et j’ai treize ans."  # codespell:ignore
+    task = DetectLanguage()
+    input = DetectLanguageInput(
+        text=text,
+        possible_languages=[Language(lang) for lang in ["en", "de"]],
+    )
+    tracer = NoOpTracer()
+    output = task.run(input, tracer)
+
+    assert output.best_fit is None