fix required() tests and add additional coverage

Author: jthrilly

lib/interviewer/utils/__tests__/field-validations.test.ts

@@ -91,7 +91,19 @@ describe('Validations', () => {
   });
   describe('required()', () => {
     const errorMessage = 'You must answer this question before continuing';
-    const subject = required();
+    const subject = required(true);
+
+    it('handles initialisation with boolean or string to determine message', () => {
+      const withBooleanMessage = required(true);
+      const withStringMessage = required('Custom message');
+
+      expect(withBooleanMessage('')).toBe(
+        'You must answer this question before continuing',
+      );
+      expect(withStringMessage('')).toBe('Custom message');
+      expect(withStringMessage('hello')).toBe(undefined);
+      expect(withBooleanMessage('hello')).toBe(undefined);
+    });
 
     it('passes for a string', () => {
       expect(subject('hello world')).toBe(undefined);

lib/interviewer/utils/field-validation.ts

@@ -43,13 +43,19 @@ const coerceArray = (value: FieldValue) => {
 // to be able to specify a string for the message in some cases. A better
 // design would probably be to have a separate validation function for
 // required that takes a message.
-export const required = (message?: string | boolean) => (value: FieldValue) => {
+export const required = (message: string | true) => (value: FieldValue) => {
   const isEmptyString = isString(value) && value.length === 0;
 
   if (isNil(value) || isEmptyString) {
-    return typeof message === 'boolean' && message === true
-      ? 'You must answer this question before continuing'
-      : message;
+    // If initialised with a string, assume required is true
+    // and return the string as the message
+    if (typeof message === 'string') {
+      return message;
+    }
+
+    // Otherwise, return the default message. Note: 'false' is not handled because
+    // we have never used it.
+    return 'You must answer this question before continuing';
   }
 
   return undefined;