diff --git a/src/protocols/bootloader.ts b/src/protocols/bootloader.ts
index c454e7d9..054da259 100644
--- a/src/protocols/bootloader.ts
+++ b/src/protocols/bootloader.ts
@@ -94,9 +94,7 @@ export function createProgramFlashRequest(
     payload: ArrayBuffer,
 ): Uint8Array {
     const size = payload.byteLength;
-    if (size > MaxProgramFlashSize) {
-        throw Error('payload is bigger than MaxProgramFlashSize');
-    }
+    assert(size <= MaxProgramFlashSize, 'payload is bigger than MaxProgramFlashSize');
     const msg = new Uint8Array(size + 6);
     const view = new DataView(msg.buffer);
     view.setUint8(0, Command.ProgramFlash);
diff --git a/src/sagas/bootloader.test.ts b/src/sagas/bootloader.test.ts
index 2d9b8991..b3210527 100644
--- a/src/sagas/bootloader.test.ts
+++ b/src/sagas/bootloader.test.ts
@@ -1,9 +1,152 @@
 import { Action } from 'redux';
 import { runSaga, stdChannel } from 'redux-saga';
-import { BootloaderResponseActionType, didReceive } from '../actions/bootloader';
+import {
+    BootloaderChecksumRequestAction,
+    BootloaderChecksumResponseAction,
+    BootloaderConnectionActionType,
+    BootloaderDisconnectRequestAction,
+    BootloaderEraseRequestAction,
+    BootloaderEraseResponseAction,
+    BootloaderErrorResponseAction,
+    BootloaderInfoRequestAction,
+    BootloaderInfoResponseAction,
+    BootloaderInitRequestAction,
+    BootloaderInitResponseAction,
+    BootloaderProgramRequestAction,
+    BootloaderProgramResponseAction,
+    BootloaderRebootRequestAction,
+    BootloaderRequestActionType,
+    BootloaderResponseActionType,
+    BootloaderStateRequestAction,
+    BootloaderStateResponseAction,
+    didReceive,
+} from '../actions/bootloader';
 import { Command, HubType, ProtectionLevel, Result } from '../protocols/bootloader';
 import bootloader from './bootloader';
 
+describe('message encoder', () => {
+    test.each([
+        [
+            'erase',
+            {
+                type: BootloaderRequestActionType.Erase,
+            } as BootloaderEraseRequestAction,
+            [
+                0x11, // erase command
+            ],
+        ],
+        [
+            'program',
+            {
+                type: BootloaderRequestActionType.Program,
+                address: 0x08005000,
+                payload: new Uint8Array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14])
+                    .buffer,
+            } as BootloaderProgramRequestAction,
+            [
+                0x22, // program command
+                0x12, // message size (payload size + 4)
+                0x00, // offset LSB
+                0x50, // .
+                0x00, // .
+                0x08, // offset MSB
+                0x01, // payload[0]
+                0x02, // payload[1]
+                0x03, // payload[2]
+                0x04, // payload[3]
+                0x05, // payload[4]
+                0x06, // payload[5]
+                0x07, // payload[6]
+                0x08, // payload[7]
+                0x09, // payload[8]
+                0x0a, // payload[9]
+                0x0b, // payload[10]
+                0x0c, // payload[11]
+                0x0d, // payload[12]
+                0x0e, // payload[13]
+            ],
+        ],
+        [
+            'reboot',
+            {
+                type: BootloaderRequestActionType.Reboot,
+            } as BootloaderRebootRequestAction,
+            [
+                0x33, // reboot command
+            ],
+        ],
+        [
+            'init',
+            {
+                type: BootloaderRequestActionType.Init,
+                firmwareSize: 100000,
+            } as BootloaderInitRequestAction,
+            [
+                0x44, // init command
+                0xa0, // size LSB
+                0x86, // .
+                0x01, // .
+                0x00, // size MSB
+            ],
+        ],
+        [
+            'info',
+            {
+                type: BootloaderRequestActionType.Info,
+            } as BootloaderInfoRequestAction,
+            [
+                0x55, // info command
+            ],
+        ],
+        [
+            'checksum',
+            {
+                type: BootloaderRequestActionType.Checksum,
+            } as BootloaderChecksumRequestAction,
+            [
+                0x66, // checksum command
+            ],
+        ],
+        [
+            'state',
+            {
+                type: BootloaderRequestActionType.State,
+            } as BootloaderStateRequestAction,
+            [
+                0x77, // state command
+            ],
+        ],
+        [
+            'disconnect',
+            {
+                type: BootloaderRequestActionType.Disconnect,
+            } as BootloaderDisconnectRequestAction,
+            [
+                0x88, // disconnect command
+            ],
+        ],
+    ])('encode %s request', async (_n, request, expected) => {
+        const channel = stdChannel();
+        const dispatched = new Array<Action>();
+        const task = runSaga(
+            {
+                channel,
+                dispatch: (action: Action) => dispatched.push(action),
+            },
+            bootloader,
+        );
+        channel.put(request);
+        task.cancel();
+        await task.toPromise();
+        const message = new Uint8Array(expected);
+        expect(dispatched[0]).toEqual({
+            type: BootloaderConnectionActionType.Send,
+            data: message,
+            withResponse: false,
+        });
+    });
+});
+
 describe('message decoder', () => {
     test.each([
         [
@@ -15,7 +158,7 @@ describe('message decoder', () => {
             {
                 type: BootloaderResponseActionType.Erase,
                 result: Result.Error,
-            },
+            } as BootloaderEraseResponseAction,
         ],
         [
             'flash',
@@ -31,7 +174,7 @@ describe('message decoder', () => {
                 type: BootloaderResponseActionType.Program,
                 checksum: 0xaa,
                 count: 100000,
-            },
+            } as BootloaderProgramResponseAction,
         ],
         [
             'init',
@@ -42,7 +185,7 @@ describe('message decoder', () => {
             {
                 type: BootloaderResponseActionType.Init,
                 result: Result.Error,
-            },
+            } as BootloaderInitResponseAction,
         ],
         [
             'info',
@@ -68,7 +211,7 @@ describe('message decoder', () => {
                 startAddress: 0x08005000,
                 endAddress: 0x0801f7ff,
                 hubType: HubType.MoveHub,
-            },
+            } as BootloaderInfoResponseAction,
         ],
         [
             'checksum',
@@ -79,7 +222,7 @@ describe('message decoder', () => {
             {
                 type: BootloaderResponseActionType.Checksum,
                 checksum: 0xaa,
-            },
+            } as BootloaderChecksumResponseAction,
         ],
         [
             'state',
@@ -90,7 +233,7 @@ describe('message decoder', () => {
             {
                 type: BootloaderResponseActionType.State,
                 level: ProtectionLevel.Level2,
-            },
+            } as BootloaderStateResponseAction,
         ],
         [
             'error',
@@ -104,7 +247,7 @@ describe('message decoder', () => {
             {
                 type: BootloaderResponseActionType.Error,
                 command: Command.GetFlashState,
-            },
+            } as BootloaderErrorResponseAction,
         ],
     ])('decode %s response', async (_n, message, expected) => {
         const response = new Uint8Array(message);