Evaluation Harness

Build systematic evaluation frameworks for LLM applications.

Golden Dataset Format [ { "id": "test_001", "category": "code_generation", "input": "Write a Python function to reverse a string", "expected_output": "def reverse_string(s: str) -> str:\n return s[::-1]", "rubric": { "correctness": 1.0, "style": 0.8, "documentation": 0.5 }, "metadata": { "difficulty": "easy", "tags": ["python", "strings"] } } ]

Scoring Rubrics from typing import Dict, Any

def score_exact_match(actual: str, expected: str) -> float: """Binary score: 1.0 if exact match, 0.0 otherwise""" return 1.0 if actual.strip() == expected.strip() else 0.0

def score_semantic_similarity(actual: str, expected: str) -> float: """Cosine similarity of embeddings""" actual_emb = get_embedding(actual) expected_emb = get_embedding(expected) return cosine_similarity(actual_emb, expected_emb)

def score_contains_keywords(actual: str, keywords: List[str]) -> float: """Percentage of required keywords present""" found = sum(1 for kw in keywords if kw.lower() in actual.lower()) return found / len(keywords)

def score_with_llm(actual: str, expected: str, rubric: Dict[str, float]) -> Dict[str, float]: """Use LLM as judge""" prompt = f""" Grade this output on a scale of 0-1 for each criterion:

Expected: {expected}
Actual: {actual}

Criteria: {', '.join(rubric.keys())}

Return JSON with scores.
"""
return json.loads(llm(prompt))

Test Runner class EvaluationHarness: def init(self, dataset_path: str): self.dataset = self.load_dataset(dataset_path) self.results = []

def run_evaluation(self, model_fn):
    for test_case in self.dataset:
        # Generate output
        actual = model_fn(test_case["input"])

        # Score
        scores = self.score_output(
            actual,
            test_case["expected_output"],
            test_case["rubric"]
        )

        # Record result
        self.results.append({
            "test_id": test_case["id"],
            "category": test_case["category"],
            "scores": scores,
            "passed": self.check_threshold(scores, test_case),
            "actual_output": actual,
        })

    return self.generate_report()

def score_output(self, actual, expected, rubric):
    return {
        "exact_match": score_exact_match(actual, expected),
        "semantic_similarity": score_semantic_similarity(actual, expected),
        **score_with_llm(actual, expected, rubric)
    }

def check_threshold(self, scores, test_case):
    min_scores = test_case.get("min_scores", {})
    for metric, threshold in min_scores.items():
        if scores.get(metric, 0) < threshold:
            return False
    return True

Thresholds & Pass Criteria

Define thresholds per category

THRESHOLDS = { "code_generation": { "correctness": 0.9, "style": 0.7, }, "summarization": { "semantic_similarity": 0.8, "brevity": 0.7, }, "classification": { "exact_match": 1.0, } }

def check_test_passed(result: Dict) -> bool: category = result["category"] thresholds = THRESHOLDS.get(category, {})

for metric, threshold in thresholds.items():
    if result["scores"].get(metric, 0) < threshold:
        return False

return True

Regression Report def generate_regression_report(baseline_results, current_results): report = { "summary": {}, "regressions": [], "improvements": [], "unchanged": 0 }

for baseline, current in zip(baseline_results, current_results):
    assert baseline["test_id"] == current["test_id"]

    baseline_passed = baseline["passed"]
    current_passed = current["passed"]

    if baseline_passed and not current_passed:
        report["regressions"].append({
            "test_id": baseline["test_id"],
            "category": baseline["category"],
            "baseline_scores": baseline["scores"],
            "current_scores": current["scores"],
        })
    elif not baseline_passed and current_passed:
        report["improvements"].append(baseline["test_id"])
    else:
        report["unchanged"] += 1

report["summary"] = {
    "total_tests": len(baseline_results),
    "regressions": len(report["regressions"]),
    "improvements": len(report["improvements"]),
    "unchanged": report["unchanged"],
}

return report

Continuous Evaluation

Run evaluation on every commit

def ci_evaluation(): harness = EvaluationHarness("golden_dataset.json") results = harness.run_evaluation(production_model)

# Check for regressions
baseline = load_baseline("baseline_results.json")
report = generate_regression_report(baseline, results)

# Fail CI if regressions
if report["summary"]["regressions"] > 0:
    print(f"❌ {report['summary']['regressions']} regressions detected!")
    sys.exit(1)

print("✅ All tests passed!")

Best Practices Representative dataset: Cover edge cases Multiple metrics: Don't rely on one score Human validation: Review LLM judge scores Version datasets: Track changes over time Automate in CI: Catch regressions early Regular updates: Add new test cases Output Checklist Golden dataset created (50+ examples) Multiple scoring functions Pass/fail thresholds defined Test runner implemented Regression comparison Report generation CI integration Baseline established