chore: add some falsy tests

Author: Marsup

lib/base.js

@@ -484,13 +484,15 @@ internals.Base = class {
                     return true;
                 }
 
-                for (const item of when.switch) {
-                    if (item.then?.isAsync()) {
-                        return true;
-                    }
+                if (when.switch) {
+                    for (const item of when.switch) {
+                        if (item.then?.isAsync()) {
+                            return true;
+                        }
 
-                    if (item.otherwise?.isAsync()) {
-                        return true;
+                        if (item.otherwise?.isAsync()) {
+                            return true;
+                        }
                     }
                 }
             }

test/isAsync.js

@@ -71,17 +71,33 @@ describe('isAsync()', () => {
             is: 'b',
             otherwise: Joi.string().external(() => {})
         }).isAsync()).to.be.true();
+        expect(Joi.any().when('a', {
+            is: 'b',
+            otherwise: Joi.string()
+        }).isAsync()).to.be.false();
         expect(Joi.any().when('a', {
             switch: [
                 { is: 'b', then: Joi.string() },
                 { is: 'c', then: Joi.number().external(() => {}), otherwise: Joi.string() }
             ]
         }).isAsync()).to.be.true();
+        expect(Joi.any().when('a', {
+            switch: [
+                { is: 'b', then: Joi.string() },
+                { is: 'c', then: Joi.number(), otherwise: Joi.string() }
+            ]
+        }).isAsync()).to.be.false();
         expect(Joi.any().when('a', {
             switch: [
                 { is: 'b', then: Joi.string() },
                 { is: 'c', then: Joi.string(), otherwise: Joi.number().external(() => {}) }
             ]
         }).isAsync()).to.be.true();
+        expect(Joi.any().when('a', {
+            switch: [
+                { is: 'b', then: Joi.string() },
+                { is: 'c', then: Joi.string(), otherwise: Joi.number() }
+            ]
+        }).isAsync()).to.be.false();
     });
 });