tests: add strings unit tests

Author: alessiofrittoli

__tests__/strings.test.ts

@@ -0,0 +1,53 @@
+import { ucFirst } from '@/strings'
+
+describe( 'ucFirst', () => {
+
+	it( 'returns the given string with first uppercase letter', () => {
+		
+		expect( ucFirst( 'some string' ) )
+			.toBe( 'Some string' )
+
+	} )
+	
+	
+	it( 'throws a TypeError when a non-stirng value is provided', () => {
+
+		// @ts-expect-error negative testing
+		expect( () => ucFirst() )
+			.toThrow( 'Cannot read properties of undefined (reading \'charAt\')' )
+		
+		// @ts-expect-error negative testing
+		expect( () => ucFirst( undefined ) )
+			.toThrow( 'Cannot read properties of undefined (reading \'charAt\')' )
+		
+		// @ts-expect-error negative testing
+		expect( () => ucFirst( null ) )
+			.toThrow( 'Cannot read properties of null (reading \'charAt\')' )
+
+		// @ts-expect-error negative testing
+		expect( () => ucFirst( false ) )
+			.toThrow( 'string.charAt is not a function' )
+
+		// @ts-expect-error negative testing
+		expect( () => ucFirst( true ) )
+			.toThrow( 'string.charAt is not a function' )
+
+		// @ts-expect-error negative testing
+		expect( () => ucFirst( 1 ) )
+			.toThrow( 'string.charAt is not a function' )
+		
+		// @ts-expect-error negative testing
+		expect( () => ucFirst( {} ) )
+			.toThrow( 'string.charAt is not a function' )
+		
+		// @ts-expect-error negative testing
+		expect( () => ucFirst( () => {} ) )
+			.toThrow( 'string.charAt is not a function' )
+		
+		// @ts-expect-error negative testing
+		expect( () => ucFirst( [] ) )
+			.toThrow( 'string.charAt is not a function' )
+
+	} )
+
+} )