test: add tests and make functions optional

Author: GerkinDev

lib/index.d.ts

@@ -642,7 +642,7 @@ declare namespace Joi {
     }
 
     interface ExpressionOptions extends ReferenceOptions {
-        functions: Record<string, (...args: unknown[]) => unknown>
+        functions?: Record<string, (...args: unknown[]) => unknown>
     }
 
     interface StringRegexOptions {

test/index.ts

@@ -67,6 +67,7 @@ validOpts = {
   messages: {
     'any.ref': str,
     'string.email': str,
+    'any.custom': Joi.x('{{.value}}')
   },
   dateFormat: 'iso',
 };
@@ -994,6 +995,8 @@ expr = Joi.expression('{{foo}}', { iterables: true });
 expr = Joi.expression('{{foo}}', { map: [['key', 'value']] });
 expr = Joi.expression('{{foo}}', { prefix: { local: '%' } });
 expr = Joi.expression('{{foo}}', { separator: '_' });
+expr = Joi.expression('{{foo}}', { functions: { foo: (...args) => 'return' } });
+expect.type<string>(Joi.expression('{{foo}}').render(42, {} as Joi.State, {}, {}))
 
 expr = Joi.x('{{foo}}');
 expr = Joi.x('{{foo}}', { adjust: (value) => value });
@@ -1003,6 +1006,8 @@ expr = Joi.x('{{foo}}', { iterables: true });
 expr = Joi.x('{{foo}}', { map: [['key', 'value']] });
 expr = Joi.x('{{foo}}', { prefix: { local: '%' } });
 expr = Joi.x('{{foo}}', { separator: '_' });
+expr = Joi.x('{{foo}}', { functions: { foo: (...args) => 'return' } });
+expect.type<string>(Joi.x('{{foo}}').render(42, {} as Joi.State, {}, {}))
 
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