diff --git a/frontend/src/AppState.test.ts b/frontend/src/AppState.test.ts
index 7283025..b094f59 100644
--- a/frontend/src/AppState.test.ts
+++ b/frontend/src/AppState.test.ts
@@ -14,7 +14,7 @@ const initialState: State = {
   position: { currentTime: 0, frame: 0, percent: 0 },
   audioSrc: '',
   videoSrc: '',
-  currentTime: 0,
+  currentTime: undefined,
   playState: PlayState.Paused,
 };
 
@@ -191,4 +191,125 @@ describe('stateReducer', () => {
       }
     );
   });
+
+  describe('waveformselectionchanged', () => {
+    describe.each([
+      {
+        name: 'paused',
+        audioSampleRate: 44100,
+        event: {
+          mode: SelectionMode.Selecting,
+          prevMode: SelectionMode.Selecting,
+          selection: { x1: 100, x2: 200 },
+        },
+        playState: PlayState.Paused,
+        position: { frame: 0, currentTime: 0, percent: 0 },
+        viewport: { start: 0, end: 88200 },
+        wantSelection: { start: 4410, end: 8820 },
+        wantCurrentTime: undefined,
+      },
+      {
+        name: 'playing, viewport 100%, selection is in progress',
+        audioSampleRate: 44100,
+        event: {
+          mode: SelectionMode.Selecting,
+          prevMode: SelectionMode.Selecting,
+          selection: { x1: 200, x2: 220 },
+        },
+        playState: PlayState.Playing,
+        position: { frame: 22000, currentTime: 0.4988, percent: 4.98 },
+        viewport: { start: 0, end: 441000 },
+        wantSelection: { start: 44100, end: 48510 },
+        wantCurrentTime: undefined,
+      },
+      {
+        name: 'playing, viewport partial, selection is in progress',
+        audioSampleRate: 44100,
+        event: {
+          mode: SelectionMode.Selecting,
+          prevMode: SelectionMode.Selecting,
+          selection: { x1: 0, x2: 100 },
+        },
+        playState: PlayState.Playing,
+        position: { frame: 22000, currentTime: 0.4988, percent: 4.98 },
+        viewport: { start: 88200, end: 176400 },
+        wantSelection: { start: 88200, end: 92610 },
+        wantCurrentTime: undefined,
+      },
+      {
+        name: 'playing, selection is ending, currFrame is before selection start',
+        audioSampleRate: 44100,
+        event: {
+          mode: SelectionMode.Normal,
+          prevMode: SelectionMode.Selecting,
+          selection: { x1: 1001, x2: 1200 },
+        },
+        playState: PlayState.Playing,
+        position: { frame: 22000, currentTime: 0.4988, percent: 4.98 },
+        viewport: { start: 0, end: 88200 },
+        wantSelection: { start: 44144, end: 52920 },
+        wantCurrentTime: 1.000997732426304,
+      },
+      {
+        name: 'playing, selection is ending, currFrame is within selection',
+        audioSampleRate: 44100,
+        event: {
+          mode: SelectionMode.Normal,
+          prevMode: SelectionMode.Selecting,
+          selection: { x1: 1001, x2: 1200 },
+        },
+        playState: PlayState.Playing,
+        position: { frame: 50000, currentTime: 1.133, percent: 11.33 },
+        viewport: { start: 0, end: 88200 },
+        wantSelection: { start: 44144, end: 52920 },
+        wantCurrentTime: undefined,
+      },
+      {
+        name: 'playing, selection is ending, currFrame is after selection end',
+        audioSampleRate: 44100,
+        event: {
+          mode: SelectionMode.Normal,
+          prevMode: SelectionMode.Selecting,
+          selection: { x1: 1001, x2: 1200 },
+        },
+        playState: PlayState.Playing,
+        position: { frame: 88200, currentTime: 2.0, percent: 20.0 },
+        viewport: { start: 0, end: 88200 },
+        wantSelection: { start: 44144, end: 52920 },
+        wantCurrentTime: 1.000997732426304,
+      },
+    ])(
+      '$name',
+      ({
+        audioSampleRate,
+        event,
+        playState,
+        position,
+        viewport,
+        wantSelection,
+        wantCurrentTime,
+      }) => {
+        it('generates the expected state', () => {
+          const mediaSet = MediaSet.fromPartial({
+            id: '123',
+            audioFrames: 441000,
+            audioSampleRate: audioSampleRate,
+          });
+          const state = stateReducer(
+            {
+              ...initialState,
+              position,
+              mediaSet,
+              playState,
+              viewport,
+            },
+            { type: 'waveformselectionchanged', event }
+          );
+
+          expect(state.selection).toEqual(wantSelection);
+          expect(state.currentTime).toEqual(wantCurrentTime);
+        });
+      }
+    );
+  });
 });