Add fuzzed property tests

Closes GH-17.

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",
@@ -54,7 +55,7 @@
     "build-mangle": "browserify . -s unistUtilIs -o unist-util-is.min.js -p tinyify",
     "build": "npm run build-bundle && npm run build-mangle",
     "test-api": "node test",
-    "test-coverage": "nyc --reporter lcov tape test.js",
+    "test-coverage": "nyc --reporter lcov tape test",
     "test-types": "dtslint .",
     "test": "npm run format && npm run build && npm run test-coverage && npm run test-types"
   },

test/index.js

@@ -0,0 +1,3 @@
+/* eslint-disable import/no-unassigned-import */
+require('./main')
+require('./property')

test.js renamed to test/main.js

@@ -1,7 +1,7 @@
 'use strict'
 
 var test = require('tape')
-var is = require('.')
+var is = require('..')
 
 test('unist-util-is', function (t) {
   var node = {type: 'strong'}

test/property.js

@@ -0,0 +1,80 @@
+'use strict'
+
+const test = require('tape')
+const fc = require('fast-check')
+const {isObject, isPlainObject, pick, cloneDeep} = require('lodash')
+const is = require('..')
+
+test('unist-util-is properties', (t) => {
+  t.plan(4)
+  t.doesNotThrow(
+    () =>
+      fc.assert(
+        fc.property(fc.record({type: fc.string({minLength: 1})}), (node) =>
+          is(node)
+        )
+      ),
+    'should see any object w/ a non-empty `type` as a node'
+  )
+
+  t.doesNotThrow(
+    () =>
+      fc.assert(
+        fc.property(
+          fc
+            .unicodeJsonObject()
+            .filter(
+              (node) => !(isPlainObject(node) && typeof node.type === 'string')
+            ),
+          (node) => !is(node)
+        )
+      ),
+    'should see any object w/o a `type` as a non-node'
+  )
+
+  t.doesNotThrow(
+    () =>
+      fc.assert(
+        fc.property(fc.record({type: fc.string({minLength: 1})}), (node) =>
+          is(node, node.type)
+        )
+      ),
+    'should match types'
+  )
+
+  t.doesNotThrow(
+    () =>
+      fc.assert(
+        fc.property(
+          fc
+            .unicodeJsonObject()
+            // Filter for JSON objects which unist can work with
+            .filter(
+              (node) =>
+                isPlainObject(node) &&
+                Object.keys(node).some((key) => !isObject(node[key]))
+            )
+            // Return node and a list with a random subset of its primitive value keys
+            .chain((node) =>
+              fc.tuple(
+                fc.constant(node),
+                fc.subarray(
+                  Object.keys(node).filter((key) => !isObject(node[key])),
+                  {minLength: 1}
+                )
+              )
+            ),
+          fc.string({minLength: 1}),
+          (nodeAndKeys, type) => {
+            const nodeProperties = nodeAndKeys[0]
+            const keys = nodeAndKeys[1]
+
+            const node = {...nodeProperties, type: type}
+            const subsetOfNode = pick(cloneDeep(node), keys)
+            return is(node, subsetOfNode)
+          }
+        )
+      ),
+    'should match partially'
+  )
+})