diff --git a/common/web/types/tests/kvk/kvk-file-writer.tests.ts b/common/web/types/tests/kvk/kvk-file-writer.tests.ts
new file mode 100644
index 00000000000..b579446cf62
--- /dev/null
+++ b/common/web/types/tests/kvk/kvk-file-writer.tests.ts
@@ -0,0 +1,325 @@
+/*
+ * Keyman is copyright (C) SIL Global. MIT License.
+ * 
+ * Created by Dr Mark C. Sinclair on 2024-12-05
+ * 
+ * Test code for kvk-file-writer.ts
+ */
+
+import 'mocha';
+import { assert } from 'chai';
+import { KvkFileWriter } from '../../src/main.js';
+import { VisualKeyboard,
+         VisualKeyboardKey,
+         VisualKeyboardFont,
+         DEFAULT_KVK_FONT
+} from '../../src/kvk/visual-keyboard.js';
+import { BUILDER_KVK_FILE,
+         BUILDER_KVK_HEADER_FLAGS,
+         BUILDER_KVK_STRING,
+         BUILDER_KVK_HEADER_IDENTIFIER,
+         BUILDER_KVK_HEADER_VERSION,
+         BUILDER_KVK_KEY,
+         BUILDER_KVK_KEY_FLAGS,
+         BUILDER_KVK_SHIFT_STATE,
+} from '../../src/kvk/kvk-file.js';
+
+const VISUAL_KEYBOARD_TEXT_COLOR = 0xFF000008;
+
+describe('Test of KVK-File-Writer', () => {
+  describe('Test of write()', () => {
+    it('can create a visual keyboard', () => {
+      const writer = new KvkFileWriter;
+      const vk = initVisualKeyboard([
+        initVisualKeyboardKey(0),
+        initVisualKeyboardKey(1),
+        initVisualKeyboardKey(2),
+      ]);
+      const file = writer.write(vk);
+      assert.isNotNull(file);
+    });
+  });
+  describe('Test of build()', () => {
+    it('can build a BUILDER_KVK_FILE', () => {
+      const vk = initVisualKeyboard([
+        initVisualKeyboardKey(0),
+        initVisualKeyboardKey(1),
+        initVisualKeyboardKey(2),
+      ]);
+      const writer = new KvkFileWriter;
+      const binary: BUILDER_KVK_FILE = writer['build'](vk);
+      checkBuilderKvkFile(binary, vk);
+    });
+    it('does not take account of the VisualKeyboard version', () => {
+      const vk_version = (BUILDER_KVK_HEADER_VERSION + 0x0100);
+      const vk = initVisualKeyboard([
+          initVisualKeyboardKey(0),
+          initVisualKeyboardKey(1),
+          initVisualKeyboardKey(2),
+        ],
+        vk_version,
+        BUILDER_KVK_HEADER_FLAGS.kvkhNone,
+        "associatedKeyboard",
+        DEFAULT_KVK_FONT,
+        DEFAULT_KVK_FONT,
+        undefined,
+      );
+      const writer = new KvkFileWriter;
+      const binary: BUILDER_KVK_FILE = writer['build'](vk);
+      checkBuilderKvkFile(binary, vk);
+    });
+    it.skip('can handle a null associatedKeyboard', () => {
+      const vk_associatedKeyboard: string = null;
+      const vk = initVisualKeyboard([
+          initVisualKeyboardKey(0),
+          initVisualKeyboardKey(1),
+          initVisualKeyboardKey(2),
+        ],
+        undefined,
+        BUILDER_KVK_HEADER_FLAGS.kvkhNone,
+        vk_associatedKeyboard,
+        DEFAULT_KVK_FONT,
+        DEFAULT_KVK_FONT,
+        undefined,
+      );
+      const writer = new KvkFileWriter;
+      const binary: BUILDER_KVK_FILE = writer['build'](vk);
+      checkBuilderKvkFile(binary, vk);
+    });
+    it.skip('can handle a null ansiFont name', () => {
+      const vk_ansiFont_name: string = null;
+      const vk = initVisualKeyboard([
+          initVisualKeyboardKey(0),
+          initVisualKeyboardKey(1),
+          initVisualKeyboardKey(2),
+        ],
+        undefined,
+        BUILDER_KVK_HEADER_FLAGS.kvkhNone,
+        "associatedKeyboard",
+        { name: vk_ansiFont_name, size: -12 },
+        DEFAULT_KVK_FONT,
+        undefined,
+      );
+      const writer = new KvkFileWriter;
+      const binary: BUILDER_KVK_FILE = writer['build'](vk);
+      checkBuilderKvkFile(binary, vk);
+    });
+    it.skip('can handle a null unicodeFont name', () => {
+      const vk_unicodeFont_name: string = null;
+      const vk = initVisualKeyboard([
+          initVisualKeyboardKey(0),
+          initVisualKeyboardKey(1),
+          initVisualKeyboardKey(2),
+        ],
+        undefined,
+        BUILDER_KVK_HEADER_FLAGS.kvkhNone,
+        "associatedKeyboard",
+        DEFAULT_KVK_FONT,
+        { name: vk_unicodeFont_name, size: -12 },
+        undefined,
+      );
+      const writer = new KvkFileWriter;
+      const binary: BUILDER_KVK_FILE = writer['build'](vk);
+      checkBuilderKvkFile(binary, vk);
+    });
+    it('can handle a null vkey', () => {
+      const vkk_vkey: number = null;
+      const vk = initVisualKeyboard([
+        initVisualKeyboardKey(
+          vkk_vkey,
+          BUILDER_KVK_KEY_FLAGS.kvkkBitmap,
+          BUILDER_KVK_SHIFT_STATE.KVKS_NORMAL,
+          "text",
+          null,
+        ),
+        initVisualKeyboardKey(1),
+        initVisualKeyboardKey(2),
+      ]);
+      const writer = new KvkFileWriter;
+      const binary: BUILDER_KVK_FILE = writer['build'](vk);
+      checkBuilderKvkFile(binary, vk);
+    });
+    it('can handle a null key flags', () => {
+      const vkk_flags: BUILDER_KVK_KEY_FLAGS = null;
+      const vk = initVisualKeyboard([
+        initVisualKeyboardKey(
+          0,
+          vkk_flags,
+          BUILDER_KVK_SHIFT_STATE.KVKS_NORMAL,
+          "text",
+          null,
+        ),
+        initVisualKeyboardKey(1),
+        initVisualKeyboardKey(2),
+      ]);
+      const writer = new KvkFileWriter;
+      const binary: BUILDER_KVK_FILE = writer['build'](vk);
+      checkBuilderKvkFile(binary, vk);
+    });
+    it('can handle a null key shift', () => {
+      const vkk_shift: BUILDER_KVK_SHIFT_STATE = null;
+      const vk = initVisualKeyboard([
+        initVisualKeyboardKey(
+          0,
+          BUILDER_KVK_KEY_FLAGS.kvkkBitmap,
+          vkk_shift,
+          "text",
+          null,
+        ),
+        initVisualKeyboardKey(1),
+        initVisualKeyboardKey(2),
+      ]);
+      const writer = new KvkFileWriter;
+      const binary: BUILDER_KVK_FILE = writer['build'](vk);
+      checkBuilderKvkFile(binary, vk);
+    });
+    it('can handle a null key text', () => {
+      const vkk_text: string = null;
+      const vk = initVisualKeyboard([
+        initVisualKeyboardKey(
+          0,
+          BUILDER_KVK_KEY_FLAGS.kvkkBitmap,
+          BUILDER_KVK_SHIFT_STATE.KVKS_NORMAL,
+          vkk_text,
+          null,
+        ),
+        initVisualKeyboardKey(1),
+        initVisualKeyboardKey(2),
+      ]);
+      const writer = new KvkFileWriter;
+      const binary: BUILDER_KVK_FILE = writer['build'](vk);
+      checkBuilderKvkFile(binary, vk);
+    });
+    it('can handle a non-null key bitmap', () => {
+      const vkk_bitmap: number[] = [0];
+      const vk = initVisualKeyboard([
+        initVisualKeyboardKey(
+          0,
+          BUILDER_KVK_KEY_FLAGS.kvkkBitmap,
+          BUILDER_KVK_SHIFT_STATE.KVKS_NORMAL,
+          "text",
+          vkk_bitmap,
+        ),
+        initVisualKeyboardKey(1),
+        initVisualKeyboardKey(2),
+      ]);
+      const writer = new KvkFileWriter;
+      const binary: BUILDER_KVK_FILE = writer['build'](vk);
+      checkBuilderKvkFile(binary, vk);
+    });
+  });
+  describe('Test of setString()', () => {
+    it('can set a BUILDER_KVK_STRING', () => {
+      const bks: BUILDER_KVK_STRING = { len: 0, str: null };
+      const writer = new KvkFileWriter;
+      const str    = "hello";
+      writer['setString'](bks, str);
+      assert.equal(bks.len, str.length + 1);
+      assert.deepEqual(bks.str, str);
+    });
+    it('can handle an empty string', () => {
+      const bks: BUILDER_KVK_STRING = { len: 0, str: null };
+      const writer = new KvkFileWriter;
+      const str    = "";
+      writer['setString'](bks, str);
+      assert.equal(bks.len, str.length + 1);
+      assert.deepEqual(bks.str, str);
+    });
+    it('throws TypeError for a null BUILDER_KVK_STRING', () => {
+      assert.throws(() => {
+        const writer = new KvkFileWriter;
+        writer['setString'](null, "");
+      }, TypeError);
+    });
+    it('throws TypeError for a null value', () => {
+      assert.throws(() => {
+        const bks: BUILDER_KVK_STRING = { len: 0, str: null };
+        const writer = new KvkFileWriter;
+        writer['setString'](bks, null);
+      }, TypeError);
+    });
+  });
+});
+
+function initVisualKeyboard(
+  vkks: VisualKeyboardKey[],
+  version: number = undefined,
+  flags: BUILDER_KVK_HEADER_FLAGS = BUILDER_KVK_HEADER_FLAGS.kvkhNone,
+  associatedKeyboard: string = "associatedKeyboard",
+  ansiFont: VisualKeyboardFont = DEFAULT_KVK_FONT,
+  unicodeFont: VisualKeyboardFont = DEFAULT_KVK_FONT,
+  underlyingLayout: string = undefined,
+): VisualKeyboard {
+  const vkh = {
+    version: version,
+    flags: flags,
+    associatedKeyboard: associatedKeyboard,
+    ansiFont: ansiFont,
+    unicodeFont: unicodeFont,
+    underlyingLayout: underlyingLayout,
+  };
+  return { header: vkh, keys: vkks };
+};
+
+function initVisualKeyboardKey(
+  vkey: number,
+  flags: BUILDER_KVK_KEY_FLAGS = BUILDER_KVK_KEY_FLAGS.kvkkBitmap,
+  shift: BUILDER_KVK_SHIFT_STATE = BUILDER_KVK_SHIFT_STATE.KVKS_NORMAL,
+  text:  string = "text",
+  bitmap: number[] = null,
+): VisualKeyboardKey {
+  const vkk: VisualKeyboardKey = {
+    vkey,
+    flags,
+    shift,
+    text,
+    bitmap: bitmap ? new Uint8Array(bitmap) : null,
+  };
+  return vkk;
+}
+
+function checkBuilderKvkFile(binary: BUILDER_KVK_FILE, vk: VisualKeyboard) {
+  assert.equal(binary.header.identifier, BUILDER_KVK_HEADER_IDENTIFIER);
+  assert.equal(binary.header.version, BUILDER_KVK_HEADER_VERSION);
+  if (vk.header.associatedKeyboard != null) {
+    assert.deepEqual(binary.header.associatedKeyboard.str, vk.header.associatedKeyboard);
+  } else {
+    assert.deepEqual(binary.header.associatedKeyboard.str, '');
+  }
+  assert.equal(binary.header.flags, vk.header.flags);
+  assert.equal(binary.header.ansiFont.color, VISUAL_KEYBOARD_TEXT_COLOR);
+  assert.equal(binary.header.ansiFont.size, vk.header.ansiFont.size);
+  if (vk.header.ansiFont.name != null) {
+    assert.deepEqual(binary.header.ansiFont.name.str, vk.header.ansiFont.name);
+  } else {
+    assert.deepEqual(binary.header.ansiFont.name.str, '');
+  }
+  assert.equal(binary.header.unicodeFont.color, VISUAL_KEYBOARD_TEXT_COLOR);
+  assert.equal(binary.header.unicodeFont.size, vk.header.unicodeFont.size);
+  if (vk.header.unicodeFont.name != null) {
+    assert.deepEqual(binary.header.unicodeFont.name.str, vk.header.unicodeFont.name);
+  } else {
+    assert.deepEqual(binary.header.unicodeFont.name.str, '');
+  }
+  for (let idx=0; idx<binary.keys.length; idx++) {
+    checkBuilderKvkKey(binary.keys[idx], vk.keys[idx])
+  }
+}
+
+function checkBuilderKvkKey(target: BUILDER_KVK_KEY, source: VisualKeyboardKey) {
+  assert.equal(target.flags, source.flags);
+  assert.equal(target.shift, source.shift);
+  assert.equal(target.vkey,  source.vkey);
+  if (source.text != null) {
+    assert.deepEqual(target.text.str, source.text);
+  } else {
+    assert.deepEqual(target.text.str, '');
+  }
+  if (source.bitmap != null) {
+    assert.equal(target.bitmapSize, source.bitmap.byteLength);
+    assert.deepEqual(target.bitmapData, Array.from(source.bitmap));
+  } else {
+    assert.equal(target.bitmapSize, 0);
+    assert.deepEqual(target.bitmapData, []);
+  }
+}
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