task 304: harden snapshot immutability after sub-agent review

1 files changed, 105 insertions, 0 deletions

diff --git a/internal/statsengine/snapshot_test.go b/internal/statsengine/snapshot_test.go
new file mode 100644
index 0000000..065eded
--- /dev/null
+++ b/internal/statsengine/snapshot_test.go
@@ -0,0 +1,105 @@
+package statsengine
+
+import "testing"
+
+func TestNewSnapshotDefensivelyCopiesSlices(t *testing.T) {
+	latency := []float64{1, 2, 3}
+	gap := []float64{4, 5, 6}
+	throughput := []float64{7, 8, 9}
+	syscalls := []SyscallSnapshot{{Name: "read", Count: 1}}
+	files := []FileSnapshot{{Path: "/tmp/a", Accesses: 2}}
+	processes := []ProcessSnapshot{{PID: 10, Comm: "cmd"}}
+	latencyBuckets := []HistogramBucketSnapshot{{Label: "[0,1)", Count: 3}}
+	gapBuckets := []HistogramBucketSnapshot{{Label: "[1,10)", Count: 4}}
+
+	s := NewSnapshot(
+		latency,
+		gap,
+		throughput,
+		syscalls,
+		files,
+		processes,
+		NewHistogramSnapshot(3, latencyBuckets),
+		NewHistogramSnapshot(4, gapBuckets),
+	)
+
+	latency[0] = 99
+	gap[0] = 99
+	throughput[0] = 99
+	syscalls[0].Name = "write"
+	files[0].Path = "/tmp/b"
+	processes[0].Comm = "mutated"
+	latencyBuckets[0].Count = 99
+	gapBuckets[0].Count = 99
+
+	if got := s.LatencySeriesNs()[0]; got != 1 {
+		t.Fatalf("latency mutated through input slice: got %v", got)
+	}
+	if got := s.GapSeriesNs()[0]; got != 4 {
+		t.Fatalf("gap mutated through input slice: got %v", got)
+	}
+	if got := s.ThroughputSeriesB()[0]; got != 7 {
+		t.Fatalf("throughput mutated through input slice: got %v", got)
+	}
+	if got := s.Syscalls()[0].Name; got != "read" {
+		t.Fatalf("syscalls mutated through input slice: got %q", got)
+	}
+	if got := s.Files()[0].Path; got != "/tmp/a" {
+		t.Fatalf("files mutated through input slice: got %q", got)
+	}
+	if got := s.Processes()[0].Comm; got != "cmd" {
+		t.Fatalf("processes mutated through input slice: got %q", got)
+	}
+	if got := s.LatencyHistogram.Buckets()[0].Count; got != 3 {
+		t.Fatalf("latency histogram mutated through input slice: got %d", got)
+	}
+	if got := s.GapHistogram.Buckets()[0].Count; got != 4 {
+		t.Fatalf("gap histogram mutated through input slice: got %d", got)
+	}
+}
+
+func TestSnapshotAccessorsReturnCopies(t *testing.T) {
+	s := NewSnapshot(
+		[]float64{1},
+		[]float64{2},
+		[]float64{3},
+		[]SyscallSnapshot{{Name: "read"}},
+		[]FileSnapshot{{Path: "/tmp/a"}},
+		[]ProcessSnapshot{{Comm: "cmd"}},
+		NewHistogramSnapshot(1, []HistogramBucketSnapshot{{Label: "a", Count: 1}}),
+		NewHistogramSnapshot(1, []HistogramBucketSnapshot{{Label: "b", Count: 1}}),
+	)
+
+	lat := s.LatencySeriesNs()
+	lat[0] = 100
+	if got := s.LatencySeriesNs()[0]; got != 1 {
+		t.Fatalf("latency accessor leaked mutability: got %v", got)
+	}
+
+	syscalls := s.Syscalls()
+	syscalls[0].Name = "write"
+	if got := s.Syscalls()[0].Name; got != "read" {
+		t.Fatalf("syscalls accessor leaked mutability: got %q", got)
+	}
+
+	buckets := s.LatencyHistogram.Buckets()
+	buckets[0].Count = 99
+	if got := s.LatencyHistogram.Buckets()[0].Count; got != 1 {
+		t.Fatalf("bucket accessor leaked mutability: got %d", got)
+	}
+}
+
+func TestNilAccessorsRemainNil(t *testing.T) {
+	s := Snapshot{}
+	if got := s.LatencySeriesNs(); got != nil {
+		t.Fatalf("expected nil latency series, got %#v", got)
+	}
+	if got := s.Syscalls(); got != nil {
+		t.Fatalf("expected nil syscalls, got %#v", got)
+	}
+
+	h := HistogramSnapshot{}
+	if got := h.Buckets(); got != nil {
+		t.Fatalf("expected nil buckets, got %#v", got)
+	}
+}