Option: fix should.js .eql() behaviour

Making Option.value a private field broke should(Option).eql() behaviour.

See: getodk#1287 / 5ef4c72

Closes getodk#1296

lib/util/option.js

@@ -38,28 +38,35 @@ class Option {
 }
 
 class Some extends Option {
-  #value;
+  // Should.js uses `for ... in` to compare objects, so while should.js is in
+  // use an Option's value property must be "enumerable".
+  //
+  // See: https://github.com/shouldjs/equal/blob/master/index.js
+  // See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties
+  //
+  // TODO revert from __please_use_get to #value when should.js is removed.
+  //#value;
 
   /* istanbul ignore next */
   constructor(value) {
     super();
-    this.#value = value;
+    this.__please_use_get = value;
   }
 
-  get() { return this.#value; }
+  get() { return this.__please_use_get; }
 
-  map(fn) { return Option.of(fn(this.#value)); }
-  filter(predicate) { return predicate(this.#value) === true ? this : none; } // eslint-disable-line no-use-before-define
+  map(fn) { return Option.of(fn(this.__please_use_get)); }
+  filter(predicate) { return predicate(this.__please_use_get) === true ? this : none; } // eslint-disable-line no-use-before-define
 
-  orNull() { return this.#value; }
-  orElse() { return this.#value; }
-  orElseGet() { return this.#value; }
-  orThrow() { return this.#value; }
+  orNull() { return this.__please_use_get; }
+  orElse() { return this.__please_use_get; }
+  orElseGet() { return this.__please_use_get; }
+  orThrow() { return this.__please_use_get; }
 
   isDefined() { return true; }
   isEmpty() { return false; }
 
-  ifDefined(consumer) { consumer(this.#value); }
+  ifDefined(consumer) { consumer(this.__please_use_get); }
 
   // Used by ramda for comparing objects.
   equals(that) {

test/unit/util/option.js

@@ -149,4 +149,40 @@ describe('(libs/FP) Option type', () => {
       });
     });
   });
+
+  describe('should.js interactions', () => {
+
+    // N.B. should.equal() is different from should.eql():
+    //
+    // * .eql(): check equality using ===
+    // * .eql(): check equality using "should-equal" module
+    //
+    // See: https://www.npmjs.com/package/should-equal
+
+    describe('should.eql()', () => {
+      [
+        true,
+        false,
+        0,
+        1,
+        '',
+        'non-empty string',
+      ].forEach(val => {
+        it(`should recognise two Options of '${val}' to be equal`, () => {
+          Option.of(val).should.eql(Option.of(val));
+        });
+      });
+
+      [
+        [ 0, 1 ],
+        [ 0, false ],
+        [ 0, '' ],
+        [ false, '' ],
+      ].forEach((a, b) => {
+        it(`should not recognise Options of '${a}' and '${b}' as equal`, () => {
+          Option.of(a).should.not.eql(Option.of(b));
+        });
+      });
+    });
+  });
 });