feat(tests): add unit tests for core modules

tests/test_helpers.py

@@ -0,0 +1,75 @@
+"""Tests for helper functions."""
+
+import pandas as pd
+import pytest
+
+from disk_checker.core.helpers import human_count, percentile_table
+
+
+class TestHumanCount:
+    """Tests for human_count function."""
+
+    def test_small_number(self):
+        """Test formatting of small numbers."""
+        assert human_count(100) == "100"
+        assert human_count(50) == "50"
+
+    def test_thousands(self):
+        """Test formatting of thousands."""
+        assert human_count(1500) == "1k"
+        assert human_count(2500) == "3k"
+
+    def test_millions(self):
+        """Test formatting of millions."""
+        assert human_count(1500000) == "1.5M"
+        assert human_count(2750000) == "2.8M"
+
+    def test_billions(self):
+        """Test formatting of billions."""
+        assert human_count(1500000000) == "1.5G"
+        assert human_count(2750000000) == "2.8G"
+
+    def test_zero(self):
+        """Test formatting of zero."""
+        assert human_count(0) == "0"
+
+    def test_position_argument_ignored(self):
+        """Test that _pos argument is ignored."""
+        assert human_count(1000, 0) == "1k"
+
+
+class TestPercentileTable:
+    """Tests for percentile_table function."""
+
+    def test_basic_percentiles(self):
+        """Test basic percentile table generation."""
+        df = pd.DataFrame({
+            "metric": ["read_clat"] * 3,
+            "latency_ns": [1000, 2000, 3000],
+            "count": [1, 2, 1],
+        })
+        result = percentile_table(df, "read_clat", "us", [50, 90])
+        assert "Metric: read_clat" in result
+        assert "total I/Os: 4" in result
+        assert "percentile" in result
+        assert "latency" in result
+
+    def test_missing_metric(self):
+        """Test percentile table with missing metric."""
+        df = pd.DataFrame({
+            "metric": ["read_clat"],
+            "latency_ns": [1000],
+            "count": [1],
+        })
+        result = percentile_table(df, "write_clat", "us", [50])
+        assert "(no data for metric write_clat)" in result
+
+    def test_unit_display(self):
+        """Test that correct unit is displayed."""
+        df = pd.DataFrame({
+            "metric": ["read_clat"],
+            "latency_ns": [1000000],  # 1ms in ns
+            "count": [1],
+        })
+        result = percentile_table(df, "read_clat", "ms", [50])
+        assert "ms" in result