[New] Utils: add isCustomComponent

packages/enzyme-test-suite/test/Utils-spec.jsx

@@ -13,8 +13,10 @@ import {
   makeOptions,
   isEmptyValue,
   renderedDive,
+  isCustomComponent,
 } from 'enzyme/build/Utils';
 import getAdapter from 'enzyme/build/getAdapter';
+import EnzymeAdapter from 'enzyme/build/EnzymeAdapter';
 import {
   flatten,
   mapNativeEventNames,
@@ -1035,4 +1037,42 @@ describe('Utils', () => {
           });
         });
     });
+
+  describe('isCustomComponent', () => {
+    class TestAdapter extends EnzymeAdapter {
+      isCustomComponent() {}
+    }
+
+    it('delegates to the adapter has method', () => {
+      const component = {};
+      const result = {};
+      const adapter = new TestAdapter();
+      sinon.stub(adapter, 'isCustomComponent').returns(result);
+
+      const actual = isCustomComponent(component, adapter);
+
+      expect(actual).to.equal(!!result);
+
+      expect(adapter.isCustomComponent).to.have.property('callCount', 1);
+      const [args] = adapter.isCustomComponent.args;
+      expect(args).to.eql([component]);
+    });
+
+    it('returns "is a function" when adapter lacks method', () => {
+      const component = {};
+      const result = {};
+      const adapter = new TestAdapter();
+      adapter.isCustomComponent = null;
+
+      expect(isCustomComponent({}, adapter)).to.equal(false);
+      expect(isCustomComponent(() => {}, adapter)).to.equal(true);
+    });
+
+    it('throws without a valid adapter', () => {
+      expect(() => isCustomComponent({})).to.throw(Error);
+      expect(() => isCustomComponent({}, null)).to.throw(Error);
+      expect(() => isCustomComponent({}, false)).to.throw(Error);
+      expect(() => isCustomComponent({}, {})).to.throw(Error);
+    });
+  });
 });

packages/enzyme/src/Utils.js

@@ -10,6 +10,7 @@ import trim from 'string.prototype.trim';
 import { get } from './configuration';
 import { childrenOfNode } from './RSTTraversal';
 import realGetAdapter from './getAdapter';
+import validateAdapter from './validateAdapter';
 
 export const ITERATOR_SYMBOL = typeof Symbol === 'function' && Symbol.iterator;
 
@@ -49,6 +50,14 @@ export function makeOptions(options) {
   };
 }
 
+export function isCustomComponent(component, adapter) {
+  validateAdapter(adapter);
+  if (adapter.isCustomComponent) {
+    return !!adapter.isCustomComponent(component);
+  }
+  return typeof component === 'function';
+}
+
 export function isCustomComponentElement(inst, adapter) {
   if (adapter.isCustomComponentElement) {
     return !!adapter.isCustomComponentElement(inst);