feat(tests): add unit tests for core modules

tests/test_extractor.py

@@ -0,0 +1,72 @@
+"""Tests for the data extraction module."""
+
+import pytest
+import pandas as pd
+from pathlib import Path
+
+from disk_checker.core.extractor import load_latency_csv
+
+
+class TestLoadLatencyCsv:
+    """Tests for load_latency_csv function."""
+
+    def test_load_valid_csv(self, sample_csv_path):
+        """Test loading a valid fio CSV file."""
+        df = load_latency_csv(str(sample_csv_path))
+        assert not df.empty
+        assert "metric" in df.columns
+        assert "latency_ns" in df.columns
+        assert "count" in df.columns
+
+    def test_returns_long_format(self, sample_csv_path):
+        """Test that output is in long format with metric column."""
+        df = load_latency_csv(str(sample_csv_path))
+        metrics = df["metric"].unique()
+        assert "read_clat" in metrics
+
+    def test_empty_csv_raises(self, empty_csv_path):
+        """Test that empty CSV raises ValueError."""
+        with pytest.raises(ValueError, match="no metric had any numeric count data"):
+            load_latency_csv(str(empty_csv_path))
+
+    def test_invalid_format_raises(self, invalid_csv_path):
+        """Test that invalid CSV format raises ValueError."""
+        with pytest.raises(ValueError):
+            load_latency_csv(str(invalid_csv_path))
+
+    def test_missing_nsec_column_raises(self, tmp_path):
+        """Test that missing nsec column raises ValueError."""
+        csv_content = "col1,col2\n1,2\n"
+        path = tmp_path / "invalid.csv"
+        path.write_text(csv_content)
+        with pytest.raises(ValueError, match="expected first column to be 'nsec'"):
+            load_latency_csv(str(path))
+
+
+@pytest.fixture
+def sample_csv_path(tmp_path):
+    """Create a sample CSV file for testing."""
+    csv_content = """nsec,read_clat_ns_count,read_clat_ns_cumulative,read_clat_ns_percentile
+19791872,1,1,0.00016775708773695687
+22413312,4,5,0.0008387854386847844
+22675456,9,14,0.0023485992283173965
+"""
+    path = tmp_path / "test.csv"
+    path.write_text(csv_content)
+    return path
+
+
+@pytest.fixture
+def empty_csv_path(tmp_path):
+    """Create an empty CSV file for testing."""
+    path = tmp_path / "empty.csv"
+    path.write_text("nsec\n")
+    return path
+
+
+@pytest.fixture
+def invalid_csv_path(tmp_path):
+    """Create an invalid CSV file for testing."""
+    path = tmp_path / "invalid.csv"
+    path.write_text("col1,col2\n1,2\n")
+    return path