Make transformer of defineParameterType optional

This is to accurately reflect actual behavior [1].

This fixes #1179 [2].

[1] cucumber/cucumber-js#2397
[2] #1179

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 All notable changes to this project will be documented in this file.
 
+## Unreleased
+
+- Fix type signature of `defineParameterType` to correctly reflect `transformer` property's optionality, fixes [#1179](https://github.com/badeball/cypress-cucumber-preprocessor/issues/1179).
+
 ## v20.0.3
 
 - Handle browser / page crash gracefully, fixes [#1172](https://github.com/badeball/cypress-cucumber-preprocessor/issues/1172).

lib/public-member-types.ts

@@ -3,7 +3,7 @@ import * as messages from "@cucumber/messages";
 export interface IParameterTypeDefinition<T, C extends Mocha.Context> {
   name: string;
   regexp: RegExp;
-  transformer: (this: C, ...match: string[]) => T;
+  transformer?: (this: C, ...match: string[]) => T;
 }
 
 export interface IRunHookOptions {

test-d/entrypoint-browser.test-d.ts

@@ -140,6 +140,11 @@ defineParameterType({
   },
 });
 
+defineParameterType({
+  name: "foo",
+  regexp: /foo/,
+});
+
 BeforeAll(function () {
   expectType<Mocha.Context>(this);
 });

test-d/entrypoint-node.test-d.ts

@@ -140,6 +140,11 @@ defineParameterType({
   },
 });
 
+defineParameterType({
+  name: "foo",
+  regexp: /foo/,
+});
+
 BeforeAll(function () {
   expectType<Mocha.Context>(this);
 });