1 files changed, 141 insertions, 0 deletions
diff --git a/internal/export/snapshot_csv_test.go b/internal/export/snapshot_csv_test.go
new file mode 100644
index 0000000..77a0c3a
--- /dev/null
+++ b/internal/export/snapshot_csv_test.go
@@ -0,0 +1,141 @@
+package export
+
+import (
+	"encoding/csv"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"ior/internal/statsengine"
+)
+
+// TestSnapshotCSVNilSnapshot verifies that SnapshotCSV writes a valid CSV file
+// with only the header and summary rows when the snapshot is nil.
+func TestSnapshotCSVNilSnapshot(t *testing.T) {
+	// Run inside a temp dir so the timestamped CSV file is automatically
+	// cleaned up after the test.
+	dir := t.TempDir()
+	origDir, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("getwd: %v", err)
+	}
+	if err := os.Chdir(dir); err != nil {
+		t.Fatalf("chdir: %v", err)
+	}
+	t.Cleanup(func() { _ = os.Chdir(origDir) })
+
+	name, err := SnapshotCSV(nil)
+	if err != nil {
+		t.Fatalf("SnapshotCSV(nil) returned error: %v", err)
+	}
+	if name == "" {
+		t.Fatal("SnapshotCSV returned empty filename")
+	}
+	if !strings.HasPrefix(filepath.Base(name), "ior-snapshot-") {
+		t.Fatalf("unexpected filename prefix: %q", name)
+	}
+
+	data, err := os.ReadFile(filepath.Join(dir, name))
+	if err != nil {
+		t.Fatalf("read csv file: %v", err)
+	}
+
+	r := csv.NewReader(strings.NewReader(string(data)))
+	records, err := r.ReadAll()
+	if err != nil {
+		t.Fatalf("parse csv: %v", err)
+	}
+
+	// Nil snapshot: expect header + 4 summary rows.
+	if len(records) < 5 {
+		t.Fatalf("expected at least 5 CSV rows, got %d", len(records))
+	}
+	if records[0][0] != "section" {
+		t.Fatalf("expected header row first cell 'section', got %q", records[0][0])
+	}
+	for _, row := range records[1:5] {
+		if row[0] != "summary" {
+			t.Fatalf("expected summary row, got section=%q", row[0])
+		}
+	}
+}
+
+// TestSnapshotCSVWithData verifies that SnapshotCSV emits syscall, file, and
+// process rows when the snapshot contains non-empty data.
+func TestSnapshotCSVWithData(t *testing.T) {
+	dir := t.TempDir()
+	origDir, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("getwd: %v", err)
+	}
+	if err := os.Chdir(dir); err != nil {
+		t.Fatalf("chdir: %v", err)
+	}
+	t.Cleanup(func() { _ = os.Chdir(origDir) })
+
+	snap := statsengine.NewSnapshot(
+		nil, nil, nil,
+		[]statsengine.SyscallSnapshot{
+			{Name: "read", Count: 10, RatePerSec: 1.5, Bytes: 4096},
+		},
+		[]statsengine.FileSnapshot{
+			{Path: "/tmp/x", Accesses: 3, BytesRead: 128, BytesWritten: 64, AvgLatencyNs: 100},
+		},
+		[]statsengine.ProcessSnapshot{
+			{PID: 42, Comm: "cat", Syscalls: 5, RatePerSec: 0.5, AvgLatencyNs: 200},
+		},
+		statsengine.NewHistogramSnapshot(1, []statsengine.HistogramBucketSnapshot{
+			{Label: "0-1µs", LowerNs: 0, UpperNs: 1000, Count: 1},
+		}),
+		statsengine.NewHistogramSnapshot(0, nil),
+	)
+
+	name, err := SnapshotCSV(&snap)
+	if err != nil {
+		t.Fatalf("SnapshotCSV returned error: %v", err)
+	}
+
+	data, err := os.ReadFile(filepath.Join(dir, name))
+	if err != nil {
+		t.Fatalf("read csv file: %v", err)
+	}
+
+	content := string(data)
+	for _, want := range []string{"syscall", "read", "file", "/tmp/x", "process", "42", "latency_hist", "0-1µs"} {
+		if !strings.Contains(content, want) {
+			t.Fatalf("expected %q in CSV output, got:\n%s", want, content)
+		}
+	}
+}
+
+// TestSnapValueHelpers verifies the nil-safe helper functions directly.
+func TestSnapValueHelpers(t *testing.T) {
+	if got := snapValue(nil, func(s *statsengine.Snapshot) uint64 { return s.TotalSyscalls }); got != 0 {
+		t.Fatalf("snapValue(nil) = %d, want 0", got)
+	}
+	if got := snapValueF(nil, func(s *statsengine.Snapshot) float64 { return s.SyscallRatePerSec }); got != 0 {
+		t.Fatalf("snapValueF(nil) = %f, want 0", got)
+	}
+	if got := trendSummary(nil, func(s *statsengine.Snapshot) statsengine.Trend { return s.LatencyTrend }); got != "stable:0.00" {
+		t.Fatalf("trendSummary(nil) = %q, want stable:0.00", got)
+	}
+
+	snap := statsengine.NewSnapshot(nil, nil, nil, nil, nil, nil,
+		statsengine.NewHistogramSnapshot(0, nil),
+		statsengine.NewHistogramSnapshot(0, nil),
+	)
+	snap.TotalSyscalls = 99
+	snap.SyscallRatePerSec = 3.14
+	snap.LatencyTrend = statsengine.Trend{Direction: statsengine.TrendRising, DeltaPercent: 12.5}
+
+	if got := snapValue(&snap, func(s *statsengine.Snapshot) uint64 { return s.TotalSyscalls }); got != 99 {
+		t.Fatalf("snapValue = %d, want 99", got)
+	}
+	if got := snapValueF(&snap, func(s *statsengine.Snapshot) float64 { return s.SyscallRatePerSec }); got != 3.14 {
+		t.Fatalf("snapValueF = %f, want 3.14", got)
+	}
+	if got := trendSummary(&snap, func(s *statsengine.Snapshot) statsengine.Trend { return s.LatencyTrend }); got != "rising:12.50" {
+		t.Fatalf("trendSummary = %q, want rising:12.50", got)
+	}
+}