algorithm: count letters (#1164)

String/test/CountLetters.test.js

@@ -0,0 +1,33 @@
+import { countLetters } from '../CountLetters'
+
+describe('CountLetters', () => {
+  it('expect throws on use wrong param', () => {
+    expect(() => countLetters(0)).toThrow()
+  })
+
+  it('expect throws when using a number in the string', () => {
+    expect(() => countLetters('h3llo')).toThrow()
+  })
+
+  it('expect throws when using a special characters in the string', () => {
+    expect(() => countLetters('hello!')).toThrow()
+  })
+
+  it('count the letters in a string. Allows lower case', () => {
+    const value = 'hello'
+    const count = countLetters(value)
+    expect(count).toEqual({ h: 1, e: 1, l: 2, o: 1 })
+  })
+
+  it('count the letters in a string. Allows upper case', () => {
+    const value = 'HELLO'
+    const count = countLetters(value)
+    expect(count).toEqual({ h: 1, e: 1, l: 2, o: 1 })
+  })
+
+  it('count the letters in a string. Allows upper and lower case', () => {
+    const value = 'HelLo'
+    const count = countLetters(value)
+    expect(count).toEqual({ h: 1, e: 1, l: 2, o: 1 })
+  })
+})