add more configuration options

src/__mocks__/config.ts

@@ -0,0 +1,5 @@
+export const config = {
+  generateRandom: Math.random,
+  skipValidations: false,
+  testSampleSize: 15,
+}

src/config.ts

@@ -1,17 +1,37 @@
-const testSampleSizeKey = Symbol('Test sample size')
+const testSampleSize = Symbol('Test sample size')
+const skipValidations = Symbol('Skip validations')
+const generateRandom = Symbol('Generate random')
 
 export const config = {
-  [testSampleSizeKey]: 15,
+  [generateRandom]: Math.random,
+  [skipValidations]: false,
+  [testSampleSize]: 15,
+
+  get generateRandom() {
+    return this[generateRandom]
+  },
+
+  set generateRandom(value: () => number) {
+    this[generateRandom] = value
+  },
+
+  get skipValidations() {
+    return this[skipValidations]
+  },
+
+  set skipValidations(value: boolean) {
+    this[skipValidations] = !!value
+  },
 
   get testSampleSize() {
-    return this[testSampleSizeKey]
+    return this[testSampleSize]
   },
 
   set testSampleSize(value: number) {
     if (value < 0) {
       throw new Error(`Test sample size cannot be negative (got ${value}).`)
     }
 
-    this[testSampleSizeKey] = Math.trunc(value)
+    this[testSampleSize] = Math.trunc(value)
   },
 }

src/validators.ts

@@ -15,20 +15,28 @@ type InstanceValidator = Validator<InstanceConstructor>
 const specialCases = [0, 1]
 
 const getRandomSampleSize = (): number => {
-  if (config.testSampleSize < specialCases.length) {
+  const { testSampleSize } = config
+
+  if (testSampleSize < specialCases.length) {
     throw new Error(
-      `Test sample size cannot be ${config.testSampleSize}, there are ${specialCases.length} special cases that must be tested. that is the minimum acceptable value.`,
+      `Test sample size cannot be ${testSampleSize}, there are ${specialCases.length} special cases that must be tested. that is the minimum acceptable value.`,
     )
   }
 
-  return config.testSampleSize - specialCases.length
+  return testSampleSize - specialCases.length
 }
 
 // An Obey of T validates using instances of T
 export class Obeys<T extends InstanceConstructor> implements InstanceValidator {
   constructor(public readonly param: Predicate<InstanceType<T>>) {}
 
   check(instance: T): ValidationResult {
+    const { skipValidations, generateRandom } = config
+
+    if (skipValidations) {
+      return new Right(true)
+    }
+
     const predicate = this.param
 
     const paramsForInstance = instance.generateData.length
@@ -60,7 +68,7 @@ export class Obeys<T extends InstanceConstructor> implements InstanceValidator {
       const params = arrayWithLength(paramsForPredicate).map(() => {
         return instance.generateData(
           // impure
-          ...arrayWithLength(paramsForInstance).map(Math.random),
+          ...arrayWithLength(paramsForInstance).map(generateRandom),
         )
       })
 

test/config.test.ts

@@ -11,3 +11,15 @@ test('Will truncate valid testSampleSizes', () => {
 
   expect(config.testSampleSize).toBe(Math.trunc(value))
 })
+
+test('Will cast skipValidations to boolean', () => {
+  // @ts-ignore
+  config.skipValidations = {}
+
+  expect(config.skipValidations).toBe(true)
+
+  // @ts-ignore
+  config.skipValidations = ''
+
+  expect(config.skipValidations).toBe(false)
+})

test/validators.test.ts

@@ -1,3 +1,5 @@
+jest.mock('../src/config')
+
 import { config } from '../src/config'
 import { Instance } from '../src/instances'
 import { Left, Right } from '../src/utils'
@@ -25,6 +27,16 @@ class SumInstance extends EqInstance {
   }
 }
 
+const defaultGenerateRandom = config.generateRandom
+const defaultSkipValidations = config.skipValidations
+const defaultTestSampleSize = config.testSampleSize
+
+beforeEach(() => {
+  config.generateRandom = defaultGenerateRandom
+  config.skipValidations = defaultSkipValidations
+  config.testSampleSize = defaultTestSampleSize
+})
+
 test('Obey returns true if the predicate holds', () => {
   const validator = obey((a: SumInstance, b: SumInstance) => {
     return a.sum(b).equals(b.sum(a))
@@ -96,6 +108,44 @@ test('Will run as many tests as it is set in the config', () => {
   expect(predicate).toBeCalledTimes(qty2)
 })
 
+test('Will not run any validation if the config says to do so', () => {
+  config.skipValidations = true
+
+  const predicate = jest.fn((a: SumInstance, b: SumInstance) => {
+    return a.sum(b).equals(b.sum(a))
+  })
+
+  const validator = obey(predicate)
+
+  expect(validator.check(SumInstance)).toBeInstanceOf(Right)
+  expect(predicate).not.toBeCalled()
+})
+
+test('Will use the given generateRandom callable', () => {
+  const random = -(2 ** 0.5)
+  config.generateRandom = () => random
+
+  const randomInstance = new SumInstance(random)
+  // special cases
+  const zero = new SumInstance(0)
+  const one = new SumInstance(1)
+
+  let anythingOtherThanExpected = false
+
+  const validator = obey((a: SumInstance, b: SumInstance) => {
+    if (
+      ![a, b].every((x) => [zero, one, randomInstance].some(x.equals.bind(x)))
+    ) {
+      anythingOtherThanExpected = true
+    }
+
+    return a.sum(b).equals(b.sum(a))
+  })
+
+  expect(validator.check(SumInstance)).toBeInstanceOf(Right)
+  expect(anythingOtherThanExpected).toBe(false)
+})
+
 const implement = (key: string) => {
   return obey((a) => key in a)
 }