kbn-expect - add .eql support for sets (elastic#200034)

## Summary

This PR adds support for asserting test equality with kbn-expect. It
also introduces some unit tests to kbn-expect in order to verify the
changes are working.

packages/kbn-expect/expect.js

@@ -647,6 +647,11 @@ function i (obj, showHidden, depth) {
       return stylize('null', 'null');
     }
 
+    // format sets like arrays
+    if (value instanceof Set) {
+      value = Array.from(value)
+    }
+
     if (isDOMElement(value)) {
       return getOuterHTML(value);
     }
@@ -930,6 +935,10 @@ expect.eql = function eql(actual, expected) {
   // to determine equivalence.
   } else if (isRegExp(actual) && isRegExp(expected)) {
     return regExpEquiv(actual, expected);
+  // If both are Sets, they should be treated equal if they have the same
+  // entries, independent of the ordering
+  } else if (actual instanceof Set && expected instanceof Set) {
+    return actual.size === expected.size && actual.difference(expected).size === 0;
   // 7.4. For all other Object pairs, including Array objects, equivalence is
   // determined by having the same number of owned properties (as verified
   // with Object.prototype.hasOwnProperty.call), the same set of keys

packages/kbn-expect/expect.test.ts

@@ -0,0 +1,47 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+// importing this package's expect as `kbnExpect` to not conflict with Jest's expect
+import kbnExpect from './expect';
+
+it('asserts that sets with same entries but different ordering are equal', async () => {
+  const setA = new Set(['a', 'b', 'c']);
+  const setB = new Set(['c', 'b', 'a']);
+
+  expect(() => {
+    kbnExpect(setA).to.eql(setB);
+  }).not.toThrow();
+  expect(() => {
+    kbnExpect(setB).to.eql(setA);
+  }).not.toThrow();
+});
+
+it('asserts that sets with same size but different entries are not equal', async () => {
+  const setA = new Set(['a', 'b', 'c']);
+  const setB = new Set(['x', 'y', 'z']);
+
+  expect(() => {
+    kbnExpect(setA).to.eql(setB);
+  }).toThrow();
+  expect(() => {
+    kbnExpect(setB).to.eql(setA);
+  }).toThrow();
+});
+
+it('asserts that sets with different size but overlapping items are not equal', async () => {
+  const setA = new Set(['a', 'b', 'c']);
+  const setB = new Set(['a', 'b']);
+
+  expect(() => {
+    kbnExpect(setA).to.eql(setB);
+  }).toThrow();
+  expect(() => {
+    kbnExpect(setB).to.eql(setA);
+  }).toThrow();
+});

packages/kbn-expect/jest.config.js

@@ -0,0 +1,14 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+module.exports = {
+  preset: '@kbn/test/jest_node',
+  rootDir: '../..',
+  roots: ['<rootDir>/packages/kbn-expect'],
+};

packages/kbn-expect/tsconfig.json

@@ -1,10 +1,14 @@
 {
   "extends": "../../tsconfig.base.json",
   "compilerOptions": {
-    "outDir": "target/types"
+    "outDir": "target/types",
+    "types": [
+      "jest",
+    ],
   },
   "include": [
-    "expect.d.ts"
+    "expect.d.ts",
+    "**/*.ts"
   ],
   "exclude": [
     "target/**/*",