diff --git a/devapp/stats_test.go b/devapp/stats_test.go
new file mode 100644
index 0000000..c15d996
--- /dev/null
+++ b/devapp/stats_test.go
@@ -0,0 +1,117 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"math"
+	"testing"
+	"time"
+
+	"golang.org/x/build/maintner"
+)
+
+func TestNewIntervalFromCL(t *testing.T) {
+	var (
+		t0 = time.Now()
+		t1 = t0.Add(1 * time.Hour)
+	)
+	testCases := []struct {
+		cl         *maintner.GerritCL
+		start, end int64
+	}{
+		{
+			cl: &maintner.GerritCL{
+				Created: t0,
+				Status:  "new",
+			},
+			start: t0.Unix(),
+			end:   math.MaxInt64,
+		},
+		{
+			cl: &maintner.GerritCL{
+				Created: t0,
+				Status:  "merged",
+				Metas: []*maintner.GerritMeta{
+					{
+						Commit: &maintner.GitCommit{
+							Msg:        "autogenerated:gerrit:merged",
+							CommitTime: t1,
+						},
+					},
+				},
+			},
+			start: t0.Unix(),
+			end:   t1.Unix(),
+		},
+		{
+			cl: &maintner.GerritCL{
+				Created: t0,
+				Status:  "abandoned",
+				Metas: []*maintner.GerritMeta{
+					{
+						Commit: &maintner.GitCommit{
+							Msg:        "autogenerated:gerrit:abandon",
+							CommitTime: t1,
+						},
+					},
+				},
+			},
+			start: t0.Unix(),
+			end:   t1.Unix(),
+		},
+	}
+
+	for _, tc := range testCases {
+		ival := newIntervalFromCL(tc.cl)
+		if got, want := ival.start, tc.start; got != want {
+			t.Errorf("start: got %d; want %d", got, want)
+		}
+		if got, want := ival.end, tc.end; got != want {
+			t.Errorf("end: got %d; want %d", got, want)
+		}
+		if got, want := ival.cl, tc.cl; got != want {
+			t.Errorf("cl: got %+v; want %+v", got, want)
+		}
+	}
+}
+
+func TestIntervalIntersection(t *testing.T) {
+	testCases := []struct {
+		interval   *clInterval
+		t0, t1     time.Time
+		intersects bool
+	}{
+		{
+			&clInterval{start: 0, end: 5},
+			time.Unix(0, 0),
+			time.Unix(10, 0),
+			true,
+		},
+		{
+			&clInterval{start: 10, end: 20},
+			time.Unix(0, 0),
+			time.Unix(10, 0),
+			true,
+		},
+		{
+			&clInterval{start: 10, end: 20},
+			time.Unix(0, 0),
+			time.Unix(9, 0),
+			false,
+		},
+		{
+			&clInterval{start: 0, end: 5},
+			time.Unix(6, 0),
+			time.Unix(10, 0),
+			false,
+		},
+	}
+
+	for _, tc := range testCases {
+		if got, want := tc.interval.intersects(tc.t0, tc.t1), tc.intersects; got != want {
+			t.Errorf("(%v).intersects(%v, %v): got %v; want %v", tc.interval, tc.t0, tc.t1, got, want)
+		}
+	}
+}