feat(core): add .nextString() random string generator method

packages/core/src/RandomEngine/index.ts

@@ -149,14 +149,15 @@ export default class RandomEngine {
       + BigInt(min) + minOffset
   }
 
-  nextString (): string {
-    return ''
-  }
+  nextString (length: number, charset: string): string {
+    const arrayLength = charset.length
+
+    let result = ''
 
-  pickString () {}
-  pickArray () {}
-  pickObject () {}
+    for (let i = 0; i < length; i++) {
+      result += charset.charAt(Math.floor(this._next() * arrayLength))
+    }
 
-  shuffleString () {}
-  shuffleArray () {}
+    return result
+  }
 }

packages/core/test/RandomEngine/next-string.test.ts

@@ -0,0 +1,107 @@
+import {
+  LENGTH,
+  CharacterStats,
+} from '@testyard/stats'
+
+import RandomEngine from '../../src/RandomEngine'
+
+class TestEngine extends RandomEngine {
+  _next() {
+    return Math.random()
+  }
+}
+
+describe('RandomEngine', () => {
+  describe('.nextString()', () => {
+    describe('length', () => {
+      test('length === 0', () => {
+        const engine = new TestEngine()
+
+        for (let i = 0; i < 1_000; i++) {
+          expect(engine.nextString(0, '')).toBe('')
+          expect(engine.nextString(0, 'abc')).toBe('')
+        }
+      })
+
+      test('length === 1', () => {
+        const engine = new TestEngine()
+
+        for (let i = 0; i < 1_000; i++) {
+          expect(engine.nextString(1, 'a')).toBe('a')
+          expect(engine.nextString(1, 'b')).toBe('b')
+          expect(engine.nextString(1, 'c')).toBe('c')
+        }
+      })
+
+      test('length === 2', () => {
+        const engine = new TestEngine()
+
+        for (let i = 0; i < 1_000; i++) {
+          expect(engine.nextString(2, 'a')).toBe('aa')
+          expect(engine.nextString(2, 'b')).toBe('bb')
+          expect(engine.nextString(2, 'c')).toBe('cc')
+        }
+      })
+
+      test('length === 3', () => {
+        const engine = new TestEngine()
+
+        for (let i = 0; i < 1_000; i++) {
+          expect(engine.nextString(3, 'a')).toBe('aaa')
+          expect(engine.nextString(3, 'b')).toBe('bbb')
+          expect(engine.nextString(3, 'c')).toBe('ccc')
+        }
+      })
+    })
+
+    describe('basics', () => {
+      test('short set of characters', () => {
+        const { add, result } = new CharacterStats()
+        const engine = new TestEngine()
+
+        for (let i = 0; i < LENGTH; i++) {
+          add(engine.nextString(10, 'abc'))
+        }
+
+        expect(result.numEntries).toBe(3)
+        expect(result.characters).toEqual(['a', 'b', 'c',])
+
+        expect(result.lowestValue).toBeGreaterThanOrEqual(0.32)
+        expect(result.highestValue).toBeLessThanOrEqual(0.35)
+        expect(result.averageValue).toBeWithin(0.32, 0.35)
+
+        expect(result.of('a')).toBeWithin(0.32, 0.35)
+        expect(result.of('b')).toBeWithin(0.32, 0.35)
+        expect(result.of('c')).toBeWithin(0.32, 0.35)
+      })
+
+      test('full set of English characters', () => {
+        const { add, result } = new CharacterStats()
+        const engine = new TestEngine()
+
+        for (let i = 0; i < LENGTH; i++) {
+          add(engine.nextString(16, 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'))
+        }
+
+        expect(result.numEntries).toBe(52)
+        expect(result.characters).toEqual([
+          'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N',
+          'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
+          'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
+          'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'
+        ])
+
+        expect(result.lowestValue).toBeGreaterThanOrEqual(0.018)
+        expect(result.highestValue).toBeLessThanOrEqual(0.021)
+        expect(result.averageValue).toBeWithin(0.018, 0.021)
+
+        expect(result.of('a')).toBeWithin(0.018, 0.021)
+        expect(result.of('A')).toBeWithin(0.018, 0.021)
+        expect(result.of('m')).toBeWithin(0.018, 0.021)
+        expect(result.of('M')).toBeWithin(0.018, 0.021)
+        expect(result.of('z')).toBeWithin(0.018, 0.021)
+        expect(result.of('Z')).toBeWithin(0.018, 0.021)
+      })
+    })
+  })
+})