refactor: add matchers to expectation dynamically (#11)

* refactor: add matchers to expectation dynamically

* feat: add toThrow

* refactor: centralize types

* docs: matchers

* refactor: MatcherReport

* chore: format before lint

* refactor: simplify negated matchers

* docs: inverse matchers

package.json

@@ -14,8 +14,8 @@
   "scripts": {
     "prepack": "yarn build",
     "prebuild": "rm -rf dist",
-    "lint": "rome check src tests && rome format src tests",
-    "lint:fix": "rome check src tests --apply && rome format src tests --write",
+    "lint": "rome format src tests && rome check src tests",
+    "lint:fix": "rome format src tests --write && rome check src tests --apply",
     "test": "ts-node ./src/runner.ts ./tests",
     "build": "tsc --project ."
   },

src/expect.ts

@@ -1,5 +1,8 @@
 import assert from 'assert'
 
+import { type ExpectBase, type Expect } from './types'
+import matchers from './matchers'
+
 class TestAssertionFailed extends Error {
 	constructor(message: string) {
 		super(message)
@@ -7,41 +10,46 @@ class TestAssertionFailed extends Error {
 	}
 }
 
-class Expectation<ValueType> {
-	value: ValueType
-	negated: boolean
+function expect<ValueType>(value: ValueType): Expect<ValueType> {
+	const expectation: ExpectBase<ValueType> = {
+		value,
+		negated: false,
+		not: {},
+		addMatcher: function (this: any, matcher: any) {
+			return (other: unknown) => {
+				const out = matcher(this.value, other)
 
-	constructor(value: ValueType) {
-		this.value = value
-		this.negated = false
+				if (!out.pass) {
+					throw new TestAssertionFailed(out.message)
+				}
+			}
+		},
 	}
+	Object.entries(matchers.matchers).forEach(([label, matcher]) => {
+		Object.defineProperty(expectation, label, {
+			value: expectation.addMatcher(matcher),
+			enumerable: true,
+		})
 
-	/*
-	 * Negates the expectation.
-	 */
-	get not() {
-		this.negated = !this.negated
-		return this
-	}
-
-	toEqual(value: ValueType) {
-		if (this.negated) {
-			assert.notDeepEqual(this.value, value, new TestAssertionFailed(`Equal! ${this.value} = ${value}`))
-		} else {
-			assert.deepEqual(this.value, value, new TestAssertionFailed(`NotEqual! ${this.value} != ${value}`))
+		if (label in matchers.matchersToInverseMap) {
+			const reverseMatcherName = matchers.matchersToInverseMap[
+				label as keyof typeof matchers.matchersToInverseMap
+			] as keyof typeof matchers.inverseMatchers
+			Object.defineProperty(expectation.not, label, {
+				value: expectation.addMatcher(matchers.inverseMatchers[reverseMatcherName]),
+				enumerable: true,
+			})
 		}
-	}
+	})
 
-	toBe(value: ValueType) {
-		const isSame = Object.is(this.value, value)
+	Object.entries(matchers.inverseMatchers).forEach(([label, matcher]) => {
+		Object.defineProperty(expectation, label, {
+			value: expectation.addMatcher(matcher),
+			enumerable: true,
+		})
+	})
 
-		if ((isSame && !this.negated) || (!isSame && this.negated)) return
-		throw new TestAssertionFailed(`NotEqual! ${this.value} ${this.negated ? '===' : '!=='} ${value}`)
-	}
-}
-
-function expect<ValueType>(value: ValueType) {
-	return new Expectation(value)
+	return expectation as Expect<ValueType>
 }
 
 export default expect

src/matchers.ts

@@ -0,0 +1,93 @@
+/*
+ * Built-in matchers
+ *
+ * All the matchers defined and exported as part of the default export
+ * of this file are available to each `expect` statement made in tests.
+ */
+import assert from 'assert'
+
+import { type MatcherReport } from './types'
+
+/*
+ * Asserts whether value and other are strictly equal.
+ */
+function toEqual(value: unknown, other: unknown): MatcherReport {
+	const output = { pass: false, message: '' }
+
+	try {
+		assert.deepEqual(value, other)
+		output.pass = true
+	} catch (e) {
+		output.message = `${value} != ${other}`
+	}
+
+	return output
+}
+
+/*
+ * Inverse of toEqual.
+ */
+function toNotEqual(value: unknown, other: unknown): MatcherReport {
+	const out = toEqual(value, other)
+
+	out.pass = !out.pass
+	out.message = out.pass ? '' : `${value} == ${other}`
+
+	return out
+}
+
+/*
+ * Asserts whether value and other are the same entity.
+ */
+function toBe(value: unknown, other: unknown): MatcherReport {
+	const isSame = Object.is(value, other)
+	return { pass: isSame, message: `${value} is not ${other}` }
+}
+
+/*
+ * Inverse ot toBe.
+ */
+function toNotBe(value: unknown, other: unknown): MatcherReport {
+	const out = toBe(value, other)
+
+	out.pass = !out.pass
+	out.message = out.pass ? '' : `${value} is ${other}`
+
+	return out
+}
+
+/*
+ * Asserts whether the provided function throws the provided error.
+ */
+function toThrow(func: () => unknown, error: Error): MatcherReport {
+	const report = { pass: false, message: '' }
+
+	try {
+		func()
+	} catch (e) {
+		report.pass = true
+	}
+
+	if (!report.pass) {
+		report.message = 'Function did not throw'
+	}
+
+	return report
+}
+
+/*
+ * Inverse of toThrow.
+ */
+function toNotThrow(func: () => unknown, error: Error): MatcherReport {
+	const out = toThrow(func, error)
+
+	out.pass = !out.pass
+	out.message = out.pass ? '' : 'Function threw exception'
+
+	return out
+}
+
+const matchers = { toEqual, toBe, toThrow }
+const inverseMatchers = { toNotEqual, toNotBe, toNotThrow }
+const matchersToInverseMap = { toEqual: 'toNotEqual', toBe: 'toNotBe', toThrow: 'toNotThrow' }
+export default { matchers, inverseMatchers, matchersToInverseMap }

src/runner.ts

@@ -143,7 +143,6 @@ function parseArgs(args: Array<string>): Args {
 		await assignTestsToWorkers(context, collectedTests)
 
 		if (server.failure) throw new Error()
-
 	} catch (e) {
 		console.log(redText('Test run failed'))
 	} finally {

src/types.ts

@@ -23,3 +23,19 @@ export interface Args {
 	runtimePath: string
 	help: boolean
 }
+
+export interface MatcherReport {
+	pass: boolean
+	message: string
+}
+
+export interface ExpectBase<ValueType> {
+	value?: ValueType
+	negated?: boolean
+	not: ExpectBase<ValueType> & any
+	addMatcher: (this: ExpectBase<ValueType> & any, matcher: any) => void
+}
+
+export type ComparisonMatcher = (value: unknown) => boolean
+
+export type Expect<ValueType> = ExpectBase<ValueType> & { [key: string]: ComparisonMatcher }

tests/expect.test.ts

@@ -57,8 +57,17 @@ describe('Identity', () => {
 	})
 })
 
-test('Stacked equality negation', () => {
-	assert.doesNotThrow(() => expect('yes').not.not.toEqual('yes'))
+describe('Exception expectation', () => {
+	test('Expects error', () => {
+		const err = new Error('err')
+		expect(() => {
+			throw err
+		}).toThrow(err)
+	})
+
+	test('Expects no error', () => {
+		expect(() => {}).not.toThrow()
+	})
 })
 
 test('Identity negation', () => {