feat: add isTrue and isFalse checks on boolean (#910)

src/boolean.js

@@ -1,5 +1,7 @@
 import inherits from './util/inherits';
 import MixedSchema from './mixed';
+import { boolean as locale } from './locale';
+import isAbsent from './util/isAbsent';
 
 export default BooleanSchema;
 
@@ -25,4 +27,28 @@ inherits(BooleanSchema, MixedSchema, {
 
     return typeof v === 'boolean';
   },
+
+  isTrue(message = locale.isValue) {
+    return this.test({
+      message,
+      name: 'is-value',
+      exclusive: true,
+      params: { value: 'true' },
+      test(value) {
+        return isAbsent(value) || value === true;
+      },
+    });
+  },
+
+  isFalse(message = locale.isValue) {
+    return this.test({
+      message,
+      name: 'is-value',
+      exclusive: true,
+      params: { value: 'false' },
+      test(value) {
+        return isAbsent(value) || value === false;
+      },
+    });
+  },
 });

src/locale.js

@@ -52,7 +52,9 @@ export let date = {
   max: '${path} field must be at earlier than ${max}',
 };
 
-export let boolean = {};
+export let boolean = {
+  isValue: '${path} field must be ${value}',
+};
 
 export let object = {
   noUnknown: '${path} field has unspecified keys: ${unknown}',

test/bool.js

@@ -56,4 +56,34 @@ describe('Boolean types', () => {
         }),
     ]);
   });
+
+  it('should check isTrue correctly', () => {
+    return Promise.all([
+      bool()
+        .isTrue()
+        .isValid(true)
+        .should.eventually()
+        .equal(true),
+      bool()
+        .isTrue()
+        .isValid(false)
+        .should.eventually()
+        .equal(false),
+    ]);
+  });
+
+  it('should check isFalse correctly', () => {
+    return Promise.all([
+      bool()
+        .isFalse()
+        .isValid(false)
+        .should.eventually()
+        .equal(true),
+      bool()
+        .isFalse()
+        .isValid(true)
+        .should.eventually()
+        .equal(false),
+    ]);
+  });
 });