[Fix] continue to support one-argument single

src/ReactWrapper.jsx

@@ -847,12 +847,14 @@ class ReactWrapper {
    * @returns {*}
    */
   single(name, fn) {
+    const fnName = typeof name === 'string' ? name : 'unknown';
+    const callback = typeof fn === 'function' ? fn : name;
     if (this.length !== 1) {
       throw new Error(
-        `Method “${name}” is only meant to be run on a single node. ${this.length} found instead.`
+        `Method “${fnName}” is only meant to be run on a single node. ${this.length} found instead.`
       );
     }
-    return fn.call(this, this.node);
+    return callback.call(this, this.node);
   }
 
   /**

src/ShallowWrapper.js

@@ -922,12 +922,14 @@ class ShallowWrapper {
    * @returns {*}
    */
   single(name, fn) {
+    const fnName = typeof name === 'string' ? name : 'unknown';
+    const callback = typeof fn === 'function' ? fn : name;
     if (this.length !== 1) {
       throw new Error(
-        `Method “${name}” is only meant to be run on a single node. ${this.length} found instead.`
+        `Method “${fnName}” is only meant to be run on a single node. ${this.length} found instead.`
       );
     }
-    return fn.call(this, this.node);
+    return callback.call(this, this.node);
   }
 
   /**

test/ReactWrapper-spec.jsx

@@ -3131,4 +3131,29 @@ describeWithDOM('mount', () => {
       expect(d1).to.equal(d);
     });
   });
+
+  describe('#single()', () => {
+    it('throws if run on multiple nodes', () => {
+      const wrapper = mount(<div><i /><i /></div>).children();
+      expect(wrapper).to.have.lengthOf(2);
+      expect(() => wrapper.single('name!')).to.throw(
+        Error,
+        'Method “name!” is only meant to be run on a single node. 2 found instead.',
+      );
+    });
+
+    it('works with a name', () => {
+      const wrapper = mount(<div />);
+      wrapper.single('foo', (node) => {
+        expect(node).to.equal(wrapper.get(0));
+      });
+    });
+
+    it('works without a name', () => {
+      const wrapper = mount(<div />);
+      wrapper.single((node) => {
+        expect(node).to.equal(wrapper.get(0));
+      });
+    });
+  });
 });

test/ShallowWrapper-spec.jsx

@@ -3717,4 +3717,29 @@ describe('shallow', () => {
       expect(d1).to.equal(d);
     });
   });
+
+  describe('#single()', () => {
+    it('throws if run on multiple nodes', () => {
+      const wrapper = shallow(<div><i /><i /></div>).children();
+      expect(wrapper).to.have.lengthOf(2);
+      expect(() => wrapper.single('name!')).to.throw(
+        Error,
+        'Method “name!” is only meant to be run on a single node. 2 found instead.',
+      );
+    });
+
+    it('works with a name', () => {
+      const wrapper = shallow(<div />);
+      wrapper.single('foo', (node) => {
+        expect(node).to.equal(wrapper.get(0));
+      });
+    });
+
+    it('works without a name', () => {
+      const wrapper = shallow(<div />);
+      wrapper.single((node) => {
+        expect(node).to.equal(wrapper.get(0));
+      });
+    });
+  });
 });