add inheritance test suite

Author: jonchurch

test/inheritance.js

@@ -0,0 +1,63 @@
+const createError = require('../index')
+var assert = require('assert')
+
+function getProtoChain (object) {
+  const chain = []
+  let proto = Object.getPrototypeOf(object)
+  while (proto) {
+    chain.push(proto.constructor.name)
+    proto = Object.getPrototypeOf(proto)
+  }
+  return chain
+}
+
+function getProtoString (object) {
+  return getProtoChain(object).join('.')
+}
+
+describe('Inheritance', () => {
+  it('Subclasses are instances of themselves', () => {
+    class CustomError extends createError.NotFound {}
+    const err = new CustomError()
+
+    assert.ok(err instanceof CustomError, `Subclass not instanceof itself: looking for CustomError ${getProtoString(err)}`)
+  })
+  it('Subclasses are instances of their ancestors', () => {
+    class CustomError extends createError.NotFound {}
+    class MoreCustom extends CustomError {}
+    const err = new MoreCustom()
+
+    assert.ok(err instanceof Error, `Subclass not instanceof its ancestor: looking for Error ${getProtoString(err)}`)
+    assert.ok(err instanceof createError.HttpError, `Subclass not instanceof its grandparent: looking for HttpError ${getProtoString(err)}`)
+    assert.ok(err instanceof createError.NotFound, `Subclass not instanceof its grandparent: looking for NotFound ${getProtoString(err)}`)
+    assert.ok(err instanceof CustomError, `Subclass not instanceof its parent: looking for CustomError ${getProtoString(err)}`)
+  })
+})
+
+describe('Inheritance without new keyword', () => {
+  it('createError returns errors that are instances of the associated status\' constructor', () => {
+    const err = createError(404, 'Custom message', { customProperty: 'custom value' })
+
+    assert.ok(err.customProperty === 'custom value', `Custom property not set: looking "for custom value", found ${err.customProperty}`)
+    assert.ok(err instanceof createError.NotFound, `Instance not instanceof itself: looking for NotFound ${getProtoString(err)}`)
+
+    const serverError = createError({ customProperty: 'custom value' })
+
+    assert.ok(serverError.customProperty === 'custom value', `Custom property not set: looking "for custom value", found ${err.customProperty}`)
+    assert.ok(serverError instanceof createError.InternalServerError, `Instance not instanceof itself: looking for InternalServerError ${getProtoString(err)}`)
+  })
+
+  it('Dynamic constructor factory functions return instances of themselves', () => {
+    const err = createError.NotFound('Not Found')
+
+    assert.ok(err instanceof createError.NotFound, `Instance not instanceof itself: looking for NotFound ${getProtoString(err)}`)
+  })
+
+  it('Dynamic constructor factory functions return instances of their ancestors', () => {
+    const err = createError.NotFound('Not Found')
+
+    assert.ok(err instanceof Error, `Subclass not instanceof its ancestor: looking for Error ${getProtoString(err)}`)
+    assert.ok(err instanceof createError.HttpError, `Subclass not instanceof its grandparent: looking for HttpError ${getProtoString(err)}`)
+  })
+})
+