diff --git a/packages/neovim/src/api/Neovim.test.ts b/packages/neovim/src/api/Neovim.test.ts
index c25d8a2f..2227bc77 100644
--- a/packages/neovim/src/api/Neovim.test.ts
+++ b/packages/neovim/src/api/Neovim.test.ts
@@ -1,5 +1,6 @@
 /* eslint-env jest */
 import * as path from 'node:path';
+import assert from 'node:assert';
 import * as testUtil from '../testUtil';
 
 describe('Neovim API', () => {
@@ -25,7 +26,7 @@ describe('Neovim API', () => {
 
       // switch buffers
       [nvim.buffer] = buffers;
-      expect(await nvim.buffer.name).toMatch(/hello\.txt$/);
+      expect(await (await nvim.buffer).name).toMatch(/hello\.txt$/);
     });
 
     it('can list runtimepaths', async () => {
@@ -218,7 +219,7 @@ describe('Neovim API', () => {
       const numWindows = (await nvim.windows).length;
       const buffer = await nvim.createBuffer(false, false);
       expect(await nvim.buffers).toHaveLength(numBuffers + 1);
-
+      assert(typeof buffer !== 'number');
       const floatingWindow = await nvim.openWindow(buffer, true, {
         relative: 'editor',
         row: 5,
@@ -227,7 +228,7 @@ describe('Neovim API', () => {
         height: 50,
       });
       expect(await nvim.windows).toHaveLength(numWindows + 1);
-
+      assert(typeof floatingWindow !== 'number');
       await nvim.windowClose(floatingWindow, true);
       expect(await nvim.windows).toHaveLength(numWindows);
     });
@@ -235,7 +236,7 @@ describe('Neovim API', () => {
     it('resizes a window', async () => {
       const numWindows = (await nvim.windows).length;
       const buffer = await nvim.createBuffer(false, false);
-
+      assert(typeof buffer !== 'number');
       const floatingWindow = await nvim.openWindow(buffer, true, {
         relative: 'editor',
         row: 5,
@@ -243,6 +244,7 @@ describe('Neovim API', () => {
         width: 10,
         height: 10,
       });
+      assert(typeof floatingWindow !== 'number');
       expect(await nvim.windows).toHaveLength(numWindows + 1);
       expect(await floatingWindow.height).toBe(10);
       expect(await floatingWindow.width).toBe(10);
diff --git a/packages/neovim/src/api/Neovim.ts b/packages/neovim/src/api/Neovim.ts
index 5929a6b5..8933f9b5 100644
--- a/packages/neovim/src/api/Neovim.ts
+++ b/packages/neovim/src/api/Neovim.ts
@@ -169,7 +169,7 @@ export class Neovim extends BaseApi {
   /**
    * Sets the current buffer
    */
-  set buffer(buffer: AsyncBuffer) {
+  set buffer(buffer: AsyncBuffer | Buffer) {
     this.request(`${this.prefix}set_current_buf`, [buffer]);
   }
 
@@ -232,7 +232,7 @@ export class Neovim extends BaseApi {
   /**
    * Sets the current tabpage
    */
-  set tabpage(tabpage: AsyncTabpage) {
+  set tabpage(tabpage: AsyncTabpage | Tabpage) {
     this.request(`${this.prefix}set_current_tabpage`, [tabpage]);
   }
 
@@ -259,7 +259,7 @@ export class Neovim extends BaseApi {
    *
    * @param win Window handle
    */
-  set window(win: AsyncWindow) {
+  set window(win: AsyncWindow | Window) {
     if (win instanceof Window) this.setWindow(win);
     else win.then(win => this.setWindow(win));
   }
diff --git a/packages/neovim/src/api/Tabpage.test.ts b/packages/neovim/src/api/Tabpage.test.ts
index 169bfcb9..15f5ec6d 100644
--- a/packages/neovim/src/api/Tabpage.test.ts
+++ b/packages/neovim/src/api/Tabpage.test.ts
@@ -1,5 +1,6 @@
 /* eslint-env jest */
 import * as testUtil from '../testUtil';
+import type { Tabpage } from './Tabpage';
 
 describe('Tabpage API', () => {
   let nvim: ReturnType<typeof testUtil.startNvim>[1];
@@ -18,7 +19,7 @@ describe('Tabpage API', () => {
   });
 
   describe('Normal API calls', () => {
-    let tabpage;
+    let tabpage: Tabpage;
 
     beforeEach(async () => {
       tabpage = await nvim.tabpage;
@@ -68,10 +69,10 @@ describe('Tabpage API', () => {
     it('logs an error when calling `getOption`', () => {
       const spy = jest.spyOn(tabpage.logger, 'error');
 
-      tabpage.getOption('option');
+      tabpage.getOption();
       expect(spy.mock.calls.length).toBe(1);
 
-      tabpage.setOption('option', 'value');
+      tabpage.setOption();
       expect(spy.mock.calls.length).toBe(2);
       spy.mockClear();
     });
diff --git a/packages/neovim/src/api/Window.test.ts b/packages/neovim/src/api/Window.test.ts
index ff272002..f59e2562 100644
--- a/packages/neovim/src/api/Window.test.ts
+++ b/packages/neovim/src/api/Window.test.ts
@@ -1,5 +1,7 @@
 /* eslint-env jest */
+import assert from 'node:assert';
 import * as testUtil from '../testUtil';
+import type { Window } from './Window';
 
 describe('Window API', () => {
   let nvim: ReturnType<typeof testUtil.startNvim>[1];
@@ -24,7 +26,7 @@ describe('Window API', () => {
   });
 
   describe('Normal API calls', () => {
-    let win;
+    let win: Window;
 
     beforeEach(async () => {
       win = await nvim.window;
@@ -51,7 +53,7 @@ describe('Window API', () => {
     });
 
     it('has same cursor position after appending a line to buffer', async () => {
-      await win.buffer.append(['test']);
+      await (await win.buffer).append(['test']);
       expect(await win.buffer.lines).toEqual(['', 'test']);
       expect(await win.cursor).toEqual([1, 0]);
     });
@@ -94,7 +96,7 @@ describe('Window API', () => {
     });
 
     it('has the right window positions in display cells', async () => {
-      let windows;
+      let windows: Awaited<typeof nvim.windows>;
       nvim.command('vsplit');
 
       // XXX If we re-use `win` without a new call to `nvim.window`,
@@ -126,6 +128,7 @@ describe('Window API', () => {
       expect(await win.getOption('list')).toBe(true);
       win.setOption('list', false);
       expect(await win.getOption('list')).toBe(false);
+      assert(list !== undefined);
       // Restore option
       win.setOption('list', list);
       expect(await win.getOption('list')).toBe(list);
@@ -167,7 +170,7 @@ describe('Window API', () => {
     });
 
     it.skip('gets current lines in buffer', async () => {
-      expect(await nvim.window.buffer.lines).toEqual(['test']);
+      expect(await (await nvim.window.buffer).lines).toEqual(['test']);
     });
   });
 });
diff --git a/packages/neovim/src/host/NvimPlugin.test.ts b/packages/neovim/src/host/NvimPlugin.test.ts
index d6174fae..672f239b 100644
--- a/packages/neovim/src/host/NvimPlugin.test.ts
+++ b/packages/neovim/src/host/NvimPlugin.test.ts
@@ -128,6 +128,7 @@ describe('NvimPlugin', () => {
       () => {},
       getFakeNvimClient()
     );
+    // @ts-expect-error Intentionally passing empty array for command arguments.
     plugin.registerCommand('MyCommand', [], {});
     expect(Object.keys(plugin.commands)).toHaveLength(0);
   });
@@ -175,7 +176,7 @@ describe('NvimPlugin', () => {
       () => {},
       getFakeNvimClient()
     );
-    const fn = arg => arg;
+    const fn = (arg: any) => arg;
 
     plugin.registerAutocmd('BufWritePre', fn, { pattern: '*', sync: true });
     plugin.registerCommand('MyCommand', fn, { sync: true });
diff --git a/packages/neovim/src/plugin/plugin.test.ts b/packages/neovim/src/plugin/plugin.test.ts
index 291fd8ea..6ff003a5 100644
--- a/packages/neovim/src/plugin/plugin.test.ts
+++ b/packages/neovim/src/plugin/plugin.test.ts
@@ -6,7 +6,7 @@ import { command as Command } from './command';
 import { autocmd as Autocmd } from './autocmd';
 import { getFakeNvimClient } from '../testUtil';
 
-const instantiateOrRun = (Fn, ...args) => {
+const instantiateOrRun = (Fn: ReturnType<typeof Plugin>, ...args: any[]) => {
   try {
     return new Fn(...args);
   } catch (err) {
@@ -36,13 +36,16 @@ describe('Plugin class decorator', () => {
   });
 
   it('decorates class methods', () => {
-    class MyClass {}
-    MyClass.prototype.testF = () => {};
-    MyClass.prototype.testC = () => {};
-    MyClass.prototype.testA = () => {};
+    class MyClass {
+      testF() {}
+
+      testC() {}
+
+      testA() {}
+    }
 
     // This is how (closeish) babel applies decorators
-    FunctionDecorator('TestF', { eval: 'test', range: 'test' })(
+    FunctionDecorator('TestF', { eval: 'test', range: [1, 10] })(
       MyClass.prototype,
       'testF'
     );
@@ -85,15 +88,18 @@ describe('Plugin class decorator', () => {
     expect(pluginObject.registerFunction).toHaveBeenCalledWith(
       'TestF',
       [instance, MyClass.prototype.testF],
-      { sync: false, eval: 'test', range: 'test' }
+      { sync: false, eval: 'test', range: [1, 10] }
     );
   });
 
   it('generates specs from decorated methods', () => {
-    class MyClass {}
-    MyClass.prototype.testF = () => {};
-    MyClass.prototype.testC = () => {};
-    MyClass.prototype.testA = () => {};
+    class MyClass {
+      testF() {}
+
+      testC() {}
+
+      testA() {}
+    }
 
     // This is how (closeish) babel applies decorators
     FunctionDecorator('TestF')(MyClass.prototype, 'testF');
diff --git a/packages/neovim/tsconfig.json b/packages/neovim/tsconfig.json
index 94e89d26..146c85e3 100644
--- a/packages/neovim/tsconfig.json
+++ b/packages/neovim/tsconfig.json
@@ -3,6 +3,6 @@
   "compilerOptions": {
     "outDir": "./lib"
   },
-  "include": ["src", "**/api/Buffer.test.ts"],
-  "exclude": ["node_modules", "__tests__", "**/*.test.ts", "examples", "lib"]
+  "include": ["src"],
+  "exclude": ["node_modules", "examples", "lib"]
 }