Add property based tests using fast-check (#62)

This commit is a follow up of the issues opened by @rix0rrr recently:
- #56
- #57
- #59

__tests__/properties.js

@@ -0,0 +1,35 @@
+import YAML from '../src/index'
+import * as fc from 'fast-check'
+
+describe('properties', () => {
+  test('parse stringified object', () => {
+    const key = fc.fullUnicodeString()
+    const values = [
+      key,
+      fc.lorem(1000, false), // words
+      fc.lorem(100, true), // sentences
+      fc.boolean(),
+      fc.integer(),
+      fc.double(),
+      fc.constantFrom(null, Number.NEGATIVE_INFINITY, Number.POSITIVE_INFINITY)
+    ]
+    const yamlArbitrary = fc.anything({ key: key, values: values })
+    const optionsArbitrary = fc.record(
+      {
+        keepBlobsInJSON: fc.boolean(),
+        keepCstNodes: fc.boolean(),
+        keepNodeTypes: fc.boolean(),
+        mapAsMap: fc.constant(false),
+        merge: fc.boolean(),
+        schema: fc.constantFrom('core', 'yaml-1.1') // ignore 'failsafe', 'json'
+      },
+      { withDeletedKeys: true }
+    )
+
+    fc.assert(
+      fc.property(yamlArbitrary, optionsArbitrary, (obj, opts) => {
+        expect(YAML.parse(YAML.stringify(obj, opts), opts)).toStrictEqual(obj)
+      })
+    )
+  })
+})

package.json

@@ -74,6 +74,7 @@
     "babel-jest": "^23.6.0",
     "babel-plugin-add-module-exports": "^1.0.0",
     "babel-plugin-trace": "^1.1.0",
+    "fast-check": "^1.8.2",
     "jest": "^23.6.0",
     "prettier": "^1.15.3"
   },