test: add property tests

Author: ChristianMurphy

package.json

@@ -34,11 +34,12 @@
     "convert.d.ts"
   ],
   "types": "index.d.ts",
-  "dependencies": {},
   "devDependencies": {
     "@types/mdast": "^3.0.0",
     "browserify": "^17.0.0",
     "dtslint": "^4.0.0",
+    "fast-check": "^2.0.0",
+    "lodash": "^4.0.0",
     "nyc": "^15.0.0",
     "prettier": "^2.0.0",
     "remark-cli": "^9.0.0",

test.js

@@ -1,6 +1,8 @@
 'use strict'
 
 var test = require('tape')
+var fc = require('fast-check')
+var _ = require('lodash')
 var is = require('.')
 
 test('unist-util-is', function (t) {
@@ -131,3 +133,66 @@ test('unist-util-is', function (t) {
 
   t.end()
 })
+
+test('unist-util-is properties', function (t) {
+  t.plan(4)
+  t.doesNotThrow(function () {
+    fc.assert(
+      fc.property(
+        fc.record({type: fc.string({minLength: 1})}),
+        function (node) {
+          return is(node)
+        }
+      )
+    )
+  }, 'should check if given node (#1)')
+
+  t.doesNotThrow(function () {
+    fc.assert(
+      fc.property(
+        fc.dictionary(fc.string(), fc.string()).filter(function (node) {
+          return typeof node.type === 'undefined'
+        }),
+        function (node) {
+          return !is(node)
+        }
+      )
+    )
+  }, 'should check if given node (#2)')
+
+  t.doesNotThrow(function () {
+    fc.assert(
+      fc.property(
+        fc.record({type: fc.string({minLength: 1})}),
+        function (node) {
+          return is(node, node.type)
+        }
+      )
+    )
+  }, 'should match types')
+
+  t.doesNotThrow(function () {
+    fc.assert(
+      fc.property(
+        fc
+          // generate an object with primitive values
+          .dictionary(
+            fc.string(),
+            fc.oneof(fc.string(), fc.integer(), fc.bigInt(), fc.boolean())
+          )
+          // object must have some keys
+          .filter(function (node) { return _.keys(node).length > 1})
+          // return node and a list with a random subset of it's keys
+          .chain(function (node) {
+            return fc.tuple(fc.constant(node), fc.subarray(_.keys(node), {minLength: 1}))
+          }),
+        fc.string({minLength: 1}),
+        function (nodeAndKeys, type) {
+          var node = nodeAndKeys[0]
+          var keys = nodeAndKeys[1]
+          return is(_.assign(node, {type: type}), _.pick(_.cloneDeep(node), keys))
+        }
+      )
+    )
+  }, 'should match partially')
+})