diff --git a/openspec/changes/multi-day-routes/tasks.md b/openspec/changes/multi-day-routes/tasks.md
index b3e184e..da35bdb 100644
--- a/openspec/changes/multi-day-routes/tasks.md
+++ b/openspec/changes/multi-day-routes/tasks.md
@@ -42,9 +42,9 @@
 
 ## 8. Testing
 
-- [ ] 8.1 Unit tests for `computeDays()`: single day (no overnight), two days, three days, empty route, single waypoint, overnight on first/last waypoint edge cases
+- [x] 8.1 Unit tests for `computeDays()`: single day (no overnight), two days, three days, empty route, single waypoint, overnight on first/last waypoint edge cases
 - [ ] 8.2 Unit tests for `overnight.ts` helpers: set/clear/check overnight on Y.Map
-- [ ] 8.3 Unit tests for GPX roundtrip: generate with `isDayBreak`, parse back, verify `isDayBreak` preserved
+- [x] 8.3 Unit tests for GPX roundtrip: generate with `isDayBreak`, parse back, verify `isDayBreak` preserved
 - [ ] 8.4 Unit tests for `dayBreaks` extraction in route update logic
 - [ ] 8.5 E2E test: add waypoints, toggle overnight on one, verify sidebar shows day breakdown with correct stats
 - [ ] 8.6 E2E test: export GPX with day breaks, verify downloaded file contains overnight metadata
diff --git a/packages/gpx/src/compute-days.test.ts b/packages/gpx/src/compute-days.test.ts
new file mode 100644
index 0000000..0702daf
--- /dev/null
+++ b/packages/gpx/src/compute-days.test.ts
@@ -0,0 +1,139 @@
+import { describe, it, expect } from "vitest";
+import { computeDays } from "./compute-days.ts";
+import type { Waypoint } from "@trails-cool/types";
+import type { TrackPoint } from "./types.ts";
+
+function makeTrack(coords: [number, number, number][]): TrackPoint[] {
+  return coords.map(([lat, lon, ele]) => ({ lat, lon, ele }));
+}
+
+describe("computeDays", () => {
+  it("returns empty array for no waypoints", () => {
+    expect(computeDays([], [[{ lat: 0, lon: 0 }]])).toEqual([]);
+  });
+
+  it("returns empty array for no tracks", () => {
+    expect(computeDays([{ lat: 0, lon: 0 }], [])).toEqual([]);
+  });
+
+  it("returns single day when no overnight waypoints", () => {
+    const waypoints: Waypoint[] = [
+      { lat: 52.52, lon: 13.405, name: "Berlin" },
+      { lat: 51.34, lon: 12.375, name: "Leipzig" },
+    ];
+    const track = makeTrack([
+      [52.52, 13.405, 34],
+      [52.0, 13.0, 50],
+      [51.34, 12.375, 113],
+    ]);
+    const days = computeDays(waypoints, [track]);
+    expect(days).toHaveLength(1);
+    expect(days[0]!.dayNumber).toBe(1);
+    expect(days[0]!.startName).toBe("Berlin");
+    expect(days[0]!.endName).toBe("Leipzig");
+    expect(days[0]!.distance).toBeGreaterThan(0);
+  });
+
+  it("splits into two days at overnight waypoint", () => {
+    const waypoints: Waypoint[] = [
+      { lat: 52.52, lon: 13.405, name: "Berlin" },
+      { lat: 51.84, lon: 12.243, name: "Dessau", isDayBreak: true },
+      { lat: 50.98, lon: 11.028, name: "Erfurt" },
+    ];
+    const track = makeTrack([
+      [52.52, 13.405, 34],
+      [52.2, 12.8, 60],
+      [51.84, 12.243, 80],
+      [51.4, 11.6, 200],
+      [50.98, 11.028, 195],
+    ]);
+    const days = computeDays(waypoints, [track]);
+    expect(days).toHaveLength(2);
+
+    expect(days[0]!.dayNumber).toBe(1);
+    expect(days[0]!.startName).toBe("Berlin");
+    expect(days[0]!.endName).toBe("Dessau");
+
+    expect(days[1]!.dayNumber).toBe(2);
+    expect(days[1]!.startName).toBe("Dessau");
+    expect(days[1]!.endName).toBe("Erfurt");
+
+    // Total distance should roughly equal sum of days
+    const totalDist = days[0]!.distance + days[1]!.distance;
+    expect(totalDist).toBeGreaterThan(0);
+  });
+
+  it("splits into three days with two overnight stops", () => {
+    const waypoints: Waypoint[] = [
+      { lat: 0, lon: 0, name: "A" },
+      { lat: 1, lon: 0, name: "B", isDayBreak: true },
+      { lat: 2, lon: 0, name: "C", isDayBreak: true },
+      { lat: 3, lon: 0, name: "D" },
+    ];
+    const track = makeTrack([
+      [0, 0, 0], [0.5, 0, 10], [1, 0, 20],
+      [1.5, 0, 30], [2, 0, 40],
+      [2.5, 0, 50], [3, 0, 60],
+    ]);
+    const days = computeDays(waypoints, [track]);
+    expect(days).toHaveLength(3);
+    expect(days[0]!.startName).toBe("A");
+    expect(days[0]!.endName).toBe("B");
+    expect(days[1]!.startName).toBe("B");
+    expect(days[1]!.endName).toBe("C");
+    expect(days[2]!.startName).toBe("C");
+    expect(days[2]!.endName).toBe("D");
+  });
+
+  it("computes ascent and descent per day", () => {
+    const waypoints: Waypoint[] = [
+      { lat: 0, lon: 0 },
+      { lat: 1, lon: 0, isDayBreak: true },
+      { lat: 2, lon: 0 },
+    ];
+    const track = makeTrack([
+      [0, 0, 100],
+      [0.5, 0, 200],  // +100 ascent
+      [1, 0, 150],     // -50 descent
+      [1.5, 0, 50],    // -100 descent
+      [2, 0, 250],     // +200 ascent
+    ]);
+    const days = computeDays(waypoints, [track]);
+    expect(days).toHaveLength(2);
+    expect(days[0]!.ascent).toBe(100);
+    expect(days[0]!.descent).toBe(50);
+    expect(days[1]!.ascent).toBe(200);
+    expect(days[1]!.descent).toBe(100);
+  });
+
+  it("handles overnight on first waypoint gracefully", () => {
+    const waypoints: Waypoint[] = [
+      { lat: 0, lon: 0, isDayBreak: true },
+      { lat: 1, lon: 0 },
+    ];
+    const track = makeTrack([[0, 0, 0], [1, 0, 100]]);
+    const days = computeDays(waypoints, [track]);
+    // First waypoint is implicit start of Day 1, isDayBreak on it creates
+    // a zero-length day followed by the real day
+    expect(days.length).toBeGreaterThanOrEqual(1);
+  });
+
+  it("handles overnight on last waypoint gracefully", () => {
+    const waypoints: Waypoint[] = [
+      { lat: 0, lon: 0 },
+      { lat: 1, lon: 0, isDayBreak: true },
+    ];
+    const track = makeTrack([[0, 0, 0], [1, 0, 100]]);
+    const days = computeDays(waypoints, [track]);
+    // Last waypoint is implicit end, isDayBreak on it = single day
+    expect(days.length).toBeGreaterThanOrEqual(1);
+  });
+
+  it("handles single waypoint", () => {
+    const waypoints: Waypoint[] = [{ lat: 0, lon: 0 }];
+    const track = makeTrack([[0, 0, 0]]);
+    const days = computeDays(waypoints, [track]);
+    // Single waypoint can't form a meaningful day with distance
+    expect(days).toHaveLength(0);
+  });
+});
diff --git a/packages/gpx/src/generate.test.ts b/packages/gpx/src/generate.test.ts
index 0eefc9f..f92fab1 100644
--- a/packages/gpx/src/generate.test.ts
+++ b/packages/gpx/src/generate.test.ts
@@ -48,4 +48,59 @@ describe("generateGpx", () => {
     expect(parsed.waypoints[0]!.name).toBe("Start");
     expect(parsed.tracks[0]).toHaveLength(2);
   });
+
+  it("emits <type>overnight</type> for isDayBreak waypoints", () => {
+    const gpx = generateGpx({
+      waypoints: [
+        { lat: 52.52, lon: 13.405, name: "Berlin" },
+        { lat: 51.84, lon: 12.243, name: "Dessau", isDayBreak: true },
+        { lat: 50.98, lon: 11.028, name: "Erfurt" },
+      ],
+    });
+    expect(gpx).toContain("<type>overnight</type>");
+    // Only Dessau should have the type element
+    expect(gpx.match(/<type>overnight<\/type>/g)).toHaveLength(1);
+  });
+
+  it("round-trips isDayBreak through generate and parse", async () => {
+    const gpx = generateGpx({
+      waypoints: [
+        { lat: 52.52, lon: 13.405, name: "Berlin" },
+        { lat: 51.84, lon: 12.243, name: "Dessau", isDayBreak: true },
+        { lat: 50.98, lon: 11.028, name: "Erfurt" },
+      ],
+      tracks: [[
+        { lat: 52.52, lon: 13.405, ele: 34 },
+        { lat: 51.84, lon: 12.243, ele: 80 },
+        { lat: 50.98, lon: 11.028, ele: 195 },
+      ]],
+    });
+    const parsed = await parseGpxAsync(gpx);
+    expect(parsed.waypoints).toHaveLength(3);
+    expect(parsed.waypoints[0]!.isDayBreak).toBeUndefined();
+    expect(parsed.waypoints[1]!.isDayBreak).toBe(true);
+    expect(parsed.waypoints[2]!.isDayBreak).toBeUndefined();
+  });
+
+  it("splits tracks by day with splitByDay option", () => {
+    const gpx = generateGpx({
+      waypoints: [
+        { lat: 0, lon: 0, name: "A" },
+        { lat: 1, lon: 0, name: "B", isDayBreak: true },
+        { lat: 2, lon: 0, name: "C" },
+      ],
+      tracks: [[
+        { lat: 0, lon: 0, ele: 0 },
+        { lat: 0.5, lon: 0, ele: 50 },
+        { lat: 1, lon: 0, ele: 100 },
+        { lat: 1.5, lon: 0, ele: 150 },
+        { lat: 2, lon: 0, ele: 200 },
+      ]],
+      splitByDay: true,
+    });
+    // Should have two <trk> elements
+    expect(gpx.match(/<trk>/g)).toHaveLength(2);
+    expect(gpx).toContain("<name>Day 1: A - B</name>");
+    expect(gpx).toContain("<name>Day 2: B - C</name>");
+  });
 });