Add a working case of custom matchers with types!

Author: dprevost-LMI

test-types/jest/customMatchers/customMatchers.d.ts

@@ -0,0 +1,11 @@
+// TODO dprevost should we review this to have the wdio namespace or maybe the expect namespace?
+// Name jest is required to augment the jest.Matchers interface
+declare namespace jest {
+    interface AsymmetricMatchers {
+        toBeCustom(): void;
+    }
+    interface Matchers<R, T> {
+        toBeCustom(): R;
+        toBeCustomPromise: T extends ChainablePromiseElement ? (expected?: object) => Promise<R> : never;
+    }
+}

test-types/jest/customMatchers/toBeCustomPromise.ts

@@ -0,0 +1,18 @@
+import type { MatcherFunction } from 'expect'
+
+const toBeCustom: MatcherFunction =
+        function (actual: ChainablePromiseElement) {
+            const pass = actual
+            if (pass) {
+                return {
+                    message: () => 'failed to be custom',
+                    pass: true,
+                }
+            }
+            return {
+                message: () => 'failed to not be custom',
+                pass: false,
+            }
+        }
+
+expect.extend({ toBeCustom })

test-types/jest/tsconfig.json

@@ -5,10 +5,16 @@
     "target": "ES2020",
     "module": "Node16",
     "skipLibCheck": true,
+    "typeRoots": [
+      "../../node_modules/",
+      "../../",
+      "./customMatchers",
+    ],    
     "types": [
       "@types/jest",
-      "../../jest.d.ts", // Needed to be after @types/jest to override the toMatchSnapshot typing
-      "@wdio/globals/types"
-    ]
+      "jest.d.ts", // Needed to be after @types/jest to override the toMatchSnapshot typing
+      "@wdio/globals/types",
+      "customMatchers.d.ts",
+    ],
   }
 }

test-types/jest/types-jest.test.ts

@@ -194,6 +194,30 @@ describe('type assertions', async () => {
         })
     })
 
+    describe('Custom matchers', () => {
+        it('should supported correctly a non-promise custom matcher', async () => {
+            expectVoid = expect('test').toBeCustom()
+            expectVoid = expect('test').not.toBeCustom()
+
+            // @ts-expect-error
+            expectPromiseVoid = expect('test').toBeCustom()
+            // @ts-expect-error
+            expectPromiseVoid = expect('test').not.toBeCustom()
+        })
+
+        it('should supported correctly a promise custom matcher with only chainableElement as actual', async () => {
+            expectPromiseVoid = expect(chainableElement).toBeCustomPromise()
+            expectPromiseVoid = expect(chainableElement).toBeCustomPromise(expect.objectContaining({}))
+
+            // @ts-expect-error
+            expect('test').toBeCustomPromise()
+            // @ts-expect-error
+            expectVoid = expect(chainableElement).toBeCustomPromise()
+            // @ts-expect-error
+            expectVoid = expect(chainableElement).toBeCustomPromise(expect.objectContaining({}))
+        })
+    })
+
     describe('toBe', () => {
 
         it('should expect void type when actual is a boolean', async () => {