Fix flow and flowRight parameter handling (#4445)

* Enable flow and flowRight tests

* Remove flow and flowRight tests for default value and shortcut fusion

* Use native rest parameters / spread operator in flow and flowRight

* Fix syntax of flow and flowRight examples

test/flow-methods.test.js

@@ -0,0 +1,53 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { add, square, noop, identity } from './utils.js';
+import head from '../head.js';
+import map from '../map.js';
+import uniq from '../uniq.js';
+import flow from '../flow.js';
+import flowRight from '../flowRight.js';
+
+const methods = {
+  flow,
+  flowRight
+}
+
+describe('flow methods', function() {
+  lodashStable.each(['flow', 'flowRight'], function(methodName) {
+    var func = methods[methodName],
+        isFlow = methodName == 'flow';
+
+    it('`_.' + methodName + '` should supply each function with the return value of the previous', function() {
+      var fixed = function(n) { return n.toFixed(1); },
+          combined = isFlow ? func(add, square, fixed) : func(fixed, square, add);
+
+      assert.strictEqual(combined(1, 2), '9.0');
+    });
+
+    it('`_.' + methodName + '` should return a new function', function() {
+      assert.notStrictEqual(func(noop), noop);
+    });
+
+    it('`_.' + methodName + '` should work with a curried function and `_.head`', function() {
+      var curried = lodashStable.curry(identity);
+
+      var combined = isFlow
+        ? func(head, curried)
+        : func(curried, head);
+
+      assert.strictEqual(combined([1]), 1);
+    });
+
+    it('`_.' + methodName + '` should work with curried functions with placeholders', function() {
+      var curried = lodashStable.curry(lodashStable.ary(map, 2), 2),
+          getProp = curried(curried.placeholder, (value) => value.a),
+          objects = [{ 'a': 1 }, { 'a': 2 }, { 'a': 1 }];
+
+      var combined = isFlow
+        ? func(getProp, uniq)
+        : func(uniq, getProp);
+
+      assert.deepStrictEqual(combined(objects), [1, 2]);
+    });
+  });
+});