test(generation): add unit tests for render_prompt

tests/test_prompting.py

@@ -0,0 +1,51 @@
+from __future__ import annotations
+from typing import Any
+import pytest
+from app.generation.prompting import render_prompt, SYSTEM_PROMPT
+
+class TokenizerWithTemplate:
+    def __init__(self, template: str | None = "some template"):
+        self.chat_template = template
+    
+    def apply_chat_template(self, messages: list[dict[str, str]], **kwargs: Any) -> str:
+        if self.chat_template is None:
+            raise ValueError("No template set")
+        return f"TEMPLATED: {messages[-1]['content']}"
+
+class TokenizerWithoutTemplate:
+    pass
+
+def test_render_prompt_with_valid_template():
+    tokenizer = TokenizerWithTemplate()
+    prompt = render_prompt(tokenizer, "Hello")
+    assert prompt == "TEMPLATED: Hello"
+
+def test_render_prompt_with_none_template():
+    # This simulates the failure case reported by the user
+    tokenizer = TokenizerWithTemplate(template=None)
+    prompt = render_prompt(tokenizer, "Hello")
+    assert "User: Hello" in prompt
+    assert "Assistant:" in prompt
+    assert SYSTEM_PROMPT in prompt
+
+def test_render_prompt_with_exception_in_apply():
+    tokenizer = TokenizerWithTemplate()
+    # Mock apply_chat_template to raise exception
+    def broken_apply(*args, **kwargs):
+        raise RuntimeError("broken")
+    tokenizer.apply_chat_template = broken_apply
+    
+    prompt = render_prompt(tokenizer, "Hello")
+    assert "User: Hello" in prompt
+
+def test_render_prompt_without_apply_method():
+    tokenizer = TokenizerWithoutTemplate()
+    prompt = render_prompt(tokenizer, "Hello")
+    assert "User: Hello" in prompt
+
+def test_render_prompt_hrm_text_fallback():
+    tokenizer = TokenizerWithoutTemplate()
+    setattr(tokenizer, "name_or_path", "sapientinc/HRM-Text-1B")
+    prompt = render_prompt(tokenizer, "Hello")
+    assert "<|im_start|><|quad_end|><|object_ref_end|><|im_end|>" in prompt
+    assert "User: Hello" in prompt