diff --git a/packages/checkbox/checkbox.test.mts b/packages/checkbox/checkbox.test.mts
index 17b169ec9..cf5b67279 100644
--- a/packages/checkbox/checkbox.test.mts
+++ b/packages/checkbox/checkbox.test.mts
@@ -644,7 +644,7 @@ describe('checkbox prompt', () => {
     const { answer, events, getScreen } = await render(checkbox, {
       message: 'Select a number',
       choices: numberedChoices,
-      validate(items: ReadonlyArray<unknown>) {
+      validate: (items: ReadonlyArray<unknown>) => {
         if (items.length !== 1) {
           return 'Please select only one choice';
         }
@@ -732,9 +732,9 @@ describe('checkbox prompt', () => {
         choices: numberedChoices,
         theme: {
           style: {
-            renderSelectedChoices(selected: { value: number }[]) {
+            renderSelectedChoices: (selected: { value: number }[]) => {
               if (selected.length > 1) {
-                return `You have selected ${selected[0].value} and ${selected.length - 1} more.`;
+                return `You have selected ${(selected[0] as { value: number }).value} and ${selected.length - 1} more.`;
               }
               return `You have selected ${selected
                 .slice(0, 1)
@@ -764,10 +764,10 @@ describe('checkbox prompt', () => {
         choices: numberedChoices,
         theme: {
           style: {
-            renderSelectedChoices(
+            renderSelectedChoices: (
               selected: { value: number }[],
               all: ({ value: number } | Separator)[],
-            ) {
+            ) => {
               return `You have selected ${selected.length} out of ${all.length} options.`;
             },
           },
diff --git a/packages/confirm/confirm.test.mts b/packages/confirm/confirm.test.mts
index e364888a4..ff36c1d48 100644
--- a/packages/confirm/confirm.test.mts
+++ b/packages/confirm/confirm.test.mts
@@ -113,7 +113,7 @@ describe('confirm prompt', () => {
   it('supports transformer option', async () => {
     const { answer, events, getScreen } = await render(confirm, {
       message: 'Do you want to proceed?',
-      transformer: (value) => (value ? 'Oui!' : 'Oh non!'),
+      transformer: (value: boolean) => (value ? 'Oui!' : 'Oh non!'),
     });
 
     expect(getScreen()).toMatchInlineSnapshot('"? Do you want to proceed? (Y/n)"');
diff --git a/packages/core/core.test.mts b/packages/core/core.test.mts
index ebc4c832c..12c97d474 100644
--- a/packages/core/core.test.mts
+++ b/packages/core/core.test.mts
@@ -54,7 +54,7 @@ describe('createPrompt()', () => {
   });
 
   it('useEffect: works with setting state at once with objects', async () => {
-    const Prompt = (config: { message: string }, done: (value: string) => void) => {
+    const Prompt = (_config: { message: string }, done: (value: string) => void) => {
       const [value, setValue] = useState([1, 2]);
 
       useEffect(() => {
@@ -518,7 +518,7 @@ describe('Error handling', () => {
   });
 
   it('surface errors in useEffect cleanup functions', async () => {
-    const Prompt = (config: object, done: (value: string) => void) => {
+    const Prompt = (_config: object, done: (value: string) => void) => {
       useEffect(() => {
         done('done');
 
@@ -537,7 +537,7 @@ describe('Error handling', () => {
   });
 
   it('prevent returning promises from useEffect hook', async () => {
-    const Prompt = (config: object, done: (value: string) => void) => {
+    const Prompt = (_config: object, done: (value: string) => void) => {
       // @ts-expect-error: Testing an invalid behavior.
       useEffect(async () => {
         done('done');
diff --git a/packages/core/src/lib/pagination/lines.test.mts b/packages/core/src/lib/pagination/lines.test.mts
index 23843f3ac..1c811f10f 100644
--- a/packages/core/src/lib/pagination/lines.test.mts
+++ b/packages/core/src/lib/pagination/lines.test.mts
@@ -1,7 +1,7 @@
 import { describe, it, expect } from 'vitest';
 import { lines } from './lines.mjs';
 
-function renderResult(result) {
+function renderResult(result: string[]) {
   return `\n${result.join('\n')}\n`;
 }
 
diff --git a/packages/editor/editor.test.mts b/packages/editor/editor.test.mts
index c39c0ebb5..defb74327 100644
--- a/packages/editor/editor.test.mts
+++ b/packages/editor/editor.test.mts
@@ -73,7 +73,7 @@ describe('editor prompt', () => {
   it('handles validation', async () => {
     const { answer, events, getScreen } = await render(editor, {
       message: 'Add a description',
-      validate(value) {
+      validate: (value: string) => {
         switch (value) {
           case '1': {
             return true;
diff --git a/packages/input/input.test.mts b/packages/input/input.test.mts
index 2fd8ceed1..236d5ddec 100644
--- a/packages/input/input.test.mts
+++ b/packages/input/input.test.mts
@@ -23,7 +23,8 @@ describe('input prompt', () => {
   it('handle transformer', async () => {
     const { answer, events, getScreen } = await render(input, {
       message: 'What is your name',
-      transformer: (value, { isFinal }) => (isFinal ? 'Transformed' : `t+${value}`),
+      transformer: (value: string, { isFinal }: { isFinal: boolean }) =>
+        isFinal ? 'Transformed' : `t+${value}`,
     });
 
     expect(getScreen()).toMatchInlineSnapshot(`"? What is your name t+"`);
@@ -39,7 +40,7 @@ describe('input prompt', () => {
   it('handle synchronous validation', async () => {
     const { answer, events, getScreen } = await render(input, {
       message: 'Answer 2 ===',
-      validate: (value) => value === '2',
+      validate: (value: string) => value === '2',
     });
 
     expect(getScreen()).toMatchInlineSnapshot(`"? Answer 2 ==="`);
@@ -65,8 +66,8 @@ describe('input prompt', () => {
   it('handle asynchronous validation', async () => {
     const { answer, events, getScreen } = await render(input, {
       message: 'Answer 2 ===',
-      validate(value) {
-        return new Promise((resolve) => {
+      validate: (value: string) => {
+        return new Promise<string | boolean>((resolve) => {
           if (value === '2') {
             resolve(true);
           } else {
@@ -198,13 +199,13 @@ describe('input prompt', () => {
   it('is theme-able', async () => {
     const { answer, events, getScreen } = await render(input, {
       message: 'Answer must be: 2',
-      validate: (value) => value === '2',
+      validate: (value?: string) => value === '2',
       theme: {
         prefix: 'Q:',
         style: {
-          message: (text) => `${text} ===`,
-          error: (text) => `!! ${text} !!`,
-          answer: (text) => `_${text}_`,
+          message: (text: string) => `${text} ===`,
+          error: (text: string) => `!! ${text} !!`,
+          answer: (text: string) => `_${text}_`,
         },
       },
     });
diff --git a/packages/number/number.test.mts b/packages/number/number.test.mts
index fa47aa2fe..d7fd4e1fa 100644
--- a/packages/number/number.test.mts
+++ b/packages/number/number.test.mts
@@ -156,7 +156,7 @@ describe('number prompt', () => {
   it('handle synchronous validation', async () => {
     const { answer, events, getScreen } = await render(number, {
       message: 'Answer 2 ===',
-      validate: (value) => value === 2,
+      validate: (value?: number) => value === 2,
     });
 
     expect(getScreen()).toMatchInlineSnapshot(`"? Answer 2 ==="`);
@@ -182,8 +182,8 @@ describe('number prompt', () => {
   it('handle asynchronous validation', async () => {
     const { answer, events, getScreen } = await render(number, {
       message: 'Answer 2 ===',
-      validate(value) {
-        return new Promise((resolve) => {
+      validate: (value?: number) => {
+        return new Promise<string | boolean>((resolve) => {
           if (value === 2) {
             resolve(true);
           } else {
@@ -320,13 +320,13 @@ describe('number prompt', () => {
   it('is theme-able', async () => {
     const { answer, events, getScreen } = await render(number, {
       message: 'Answer must be: 2',
-      validate: (value) => value === 2,
+      validate: (value?: number) => value === 2,
       theme: {
         prefix: 'Q:',
         style: {
-          message: (text) => `${text} ===`,
-          error: (text) => `!! ${text} !!`,
-          answer: (text) => `_${text}_`,
+          message: (text: string) => `${text} ===`,
+          error: (text: string) => `!! ${text} !!`,
+          answer: (text: string) => `_${text}_`,
         },
       },
     });
diff --git a/packages/password/password.test.mts b/packages/password/password.test.mts
index 832844cb5..7a1093ec6 100644
--- a/packages/password/password.test.mts
+++ b/packages/password/password.test.mts
@@ -64,7 +64,7 @@ describe('password prompt', () => {
     const { answer, events, getScreen } = await render(password, {
       message: 'Enter your password',
       mask: true,
-      validate: (value) => value.length >= 8,
+      validate: (value: string) => value.length >= 8,
     });
 
     expect(getScreen()).toMatchInlineSnapshot(`"? Enter your password"`);
diff --git a/packages/prompts/prompts.test.mts b/packages/prompts/prompts.test.mts
index 6367989be..3c0c723ff 100644
--- a/packages/prompts/prompts.test.mts
+++ b/packages/prompts/prompts.test.mts
@@ -29,9 +29,11 @@ describe('@inquirer/prompts', () => {
 /**
  * Type assertions to validate the interfaces.
  */
-Expect<
-  Equal<
-    Parameters<typeof checkbox>[0]['theme']['helpMode'],
-    Parameters<typeof select>[0]['theme']['helpMode']
-  >
->;
+export interface Test {
+  1: Expect<
+    Equal<
+      NonNullable<Parameters<typeof checkbox>[0]['theme']>['helpMode'],
+      NonNullable<Parameters<typeof select>[0]['theme']>['helpMode']
+    >
+  >;
+}
diff --git a/packages/select/select.test.mts b/packages/select/select.test.mts
index b3f09b26e..87da489c5 100644
--- a/packages/select/select.test.mts
+++ b/packages/select/select.test.mts
@@ -16,7 +16,7 @@ const numberedChoices = [
   { value: 10 },
   { value: 11 },
   { value: 12 },
-];
+] as const;
 
 afterEach(() => {
   vi.useRealTimers();
diff --git a/packages/testing/src/index.mts b/packages/testing/src/index.mts
index 888d792ab..dd47202e9 100644
--- a/packages/testing/src/index.mts
+++ b/packages/testing/src/index.mts
@@ -2,7 +2,7 @@ import { Stream } from 'node:stream';
 import MuteStream from 'mute-stream';
 import stripAnsi from 'strip-ansi';
 import ansiEscapes from 'ansi-escapes';
-import type { Prompt } from '@inquirer/type';
+import type { Prompt, Context } from '@inquirer/type';
 
 const ignoredAnsi = new Set([ansiEscapes.cursorHide, ansiEscapes.cursorShow]);
 
@@ -42,11 +42,11 @@ class BufferedStream extends Stream.Writable {
   }
 }
 
-export async function render<TestedPrompt extends Prompt<unknown, unknown>>(
-  prompt: TestedPrompt,
-  props: Parameters<TestedPrompt>[0],
-  options?: Parameters<TestedPrompt>[1],
-) {
+export async function render<
+  const Props,
+  const Value,
+  const TestedPrompt extends Prompt<Value, Props>,
+>(prompt: TestedPrompt, props: Props, options?: Context) {
   const input = new MuteStream();
   input.unmute();
 
diff --git a/tsconfig.test.json b/tsconfig.test.json
new file mode 100644
index 000000000..a7f118e25
--- /dev/null
+++ b/tsconfig.test.json
@@ -0,0 +1,13 @@
+{
+  "extends": "./tsconfig.json",
+  "include": ["**/*.test.mts"],
+  "exclude": ["packages/inquirer/test/**"],
+  "compilerOptions": {
+    "lib": ["es2023"],
+    "target": "es2022",
+    "module": "NodeNext",
+    "moduleResolution": "nodenext",
+    "skipLibCheck": true,
+    "noEmit": true
+  }
+}