feat(utils): add type helpers for lower/upper case conversions

Author: matejchalk

eslint.config.js

@@ -93,6 +93,12 @@ export default tseslint.config(
       ],
     },
   },
+  {
+    files: ['**/*.type.test.ts'],
+    rules: {
+      'vitest/expect-expect': 'off',
+    },
+  },
   {
     files: ['**/*.json'],
     languageOptions: { parser: jsoncParser },

packages/utils/src/index.ts

@@ -3,8 +3,10 @@ export {
   camelCaseToKebabCase,
   capitalize,
   kebabCaseToCamelCase,
+  lowercase,
   toSentenceCase,
   toTitleCase,
+  uppercase,
 } from './lib/case-conversions.js';
 export { filesCoverageToTree, type FileCoverage } from './lib/coverage-tree.js';
 export { createRunnerFiles } from './lib/create-runner-files.js';

packages/utils/src/lib/case-conversion.type.test.ts

@@ -1,7 +1,7 @@
 import { assertType, describe, expectTypeOf, it } from 'vitest';
+import { lowercase, uppercase } from './case-conversions.js';
 import type { CamelCaseToKebabCase, KebabCaseToCamelCase } from './types.js';
 
-/* eslint-disable vitest/expect-expect */
 describe('CamelCaseToKebabCase', () => {
   // ✅ CamelCase → kebab-case Type Tests
 
@@ -60,4 +60,37 @@ describe('CamelCaseToKebabCase', () => {
     assertType<KebabCaseToCamelCase<'this-Is-Wrong'>>();
   });
 });
-/* eslint-enable vitest/expect-expect */
+
+describe('lowercase', () => {
+  it('converts string literal to lowercased literal', () => {
+    expectTypeOf(lowercase('Warning' as const)).toEqualTypeOf<'warning'>();
+  });
+
+  it('converts enum value to lowercased string literal', () => {
+    enum Severity {
+      Warning = 'Warning',
+    }
+    expectTypeOf(lowercase(Severity.Warning)).toEqualTypeOf<'warning'>();
+  });
+
+  it('converts string to string', () => {
+    expectTypeOf(lowercase('hello, world')).toBeString();
+  });
+});
+
+describe('uppercase', () => {
+  it('converts string literal to uppercased literal', () => {
+    expectTypeOf(uppercase('Warning' as const)).toEqualTypeOf<'WARNING'>();
+  });
+
+  it('converts enum value to uppercased string literal', () => {
+    enum Severity {
+      Warning = 'Warning',
+    }
+    expectTypeOf(uppercase(Severity.Warning)).toEqualTypeOf<'WARNING'>();
+  });
+
+  it('converts string to string', () => {
+    expectTypeOf(uppercase('hello, world')).toBeString();
+  });
+});

packages/utils/src/lib/case-conversions.ts

@@ -97,5 +97,13 @@ export function toSentenceCase(input: string): string {
 }
 
 export function capitalize<T extends string>(text: T): Capitalize<T> {
-  return `${text.charAt(0).toLocaleUpperCase()}${text.slice(1).toLowerCase()}` as Capitalize<T>;
+  return `${text.charAt(0).toUpperCase()}${text.slice(1).toLowerCase()}` as Capitalize<T>;
+}
+
+export function lowercase<T extends string>(text: T): Lowercase<T> {
+  return text.toLowerCase() as Lowercase<T>;
+}
+
+export function uppercase<T extends string>(text: T): Uppercase<T> {
+  return text.toUpperCase() as Uppercase<T>;
 }

packages/utils/src/lib/case-conversions.unit.test.ts

@@ -3,8 +3,10 @@ import {
   camelCaseToKebabCase,
   capitalize,
   kebabCaseToCamelCase,
+  lowercase,
   toSentenceCase,
   toTitleCase,
+  uppercase,
 } from './case-conversions.js';
 
 describe('capitalize', () => {
@@ -25,6 +27,18 @@ describe('capitalize', () => {
   });
 });
 
+describe('lowercase', () => {
+  it('should convert string to lower case', () => {
+    expect(lowercase('Warning')).toBe('warning');
+  });
+});
+
+describe('uppercase', () => {
+  it('should convert string to upper case', () => {
+    expect(uppercase('Warning')).toBe('WARNING');
+  });
+});
+
 describe('kebabCaseToCamelCase', () => {
   it('should convert simple kebab-case to camelCase', () => {
     expect(kebabCaseToCamelCase('hello-world')).toBe('helloWorld');

packages/utils/vitest.unit.config.ts

@@ -19,7 +19,10 @@ export default defineConfig({
       exclude: ['mocks/**', 'perf/**', '**/types.ts'],
     },
     environment: 'node',
-    include: ['src/**/*.unit.test.{js,mjs,cjs,ts,mts,cts,jsx,tsx}'],
+    include: ['src/**/*.{unit,type}.test.{js,mjs,cjs,ts,mts,cts,jsx,tsx}'],
+    typecheck: {
+      include: ['**/*.type.test.ts'],
+    },
     globalSetup: ['../../global-setup.ts'],
     setupFiles: [
       '../../testing/test-setup/src/lib/cliui.mock.ts',