[APM] adding unit test on transaction detail link (#138324)

x-pack/plugins/apm/public/components/shared/links/apm/transaction_detail_link.test.tsx

@@ -0,0 +1,72 @@
+/*
+ * 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; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+import { TransactionDetailLink } from './transaction_detail_link';
+import { createMemoryHistory } from 'history';
+import React from 'react';
+import { Router } from 'react-router-dom';
+import { MockApmPluginContextWrapper } from '../../../../context/apm_plugin/mock_apm_plugin_context';
+import { render } from '@testing-library/react';
+
+const history = createMemoryHistory();
+
+function Wrapper({ children }: { children: React.ReactElement }) {
+  return (
+    <MockApmPluginContextWrapper>
+      <Router history={history}>{children}</Router>
+    </MockApmPluginContextWrapper>
+  );
+}
+
+describe('TransactionDetailLink', () => {
+  function getHref(container: HTMLElement) {
+    return ((container as HTMLDivElement).children[0] as HTMLAnchorElement)
+      .href;
+  }
+  describe('With comparison in the url', () => {
+    it('returns comparison defined in the url', () => {
+      const { container } = render(
+        <Wrapper>
+          <TransactionDetailLink
+            serviceName="foo"
+            transactionName="bar"
+            transactionType="request"
+            comparisonEnabled
+            offset="1w"
+            traceId="baz"
+            transactionId="123"
+          >
+            Transaction
+          </TransactionDetailLink>
+        </Wrapper>
+      );
+      expect(getHref(container)).toEqual(
+        'http://localhost/basepath/app/apm/services/foo/transactions/view?traceId=baz&transactionId=123&transactionName=bar&transactionType=request&comparisonEnabled=true&offset=1w'
+      );
+    });
+  });
+
+  describe('use default comparison', () => {
+    it('returns default comparison', () => {
+      const { container } = render(
+        <Wrapper>
+          <TransactionDetailLink
+            serviceName="foo"
+            transactionName="bar"
+            transactionType="request"
+            traceId="baz"
+            transactionId="123"
+          >
+            Transaction
+          </TransactionDetailLink>
+        </Wrapper>
+      );
+      expect(getHref(container)).toEqual(
+        'http://localhost/basepath/app/apm/services/foo/transactions/view?traceId=baz&transactionId=123&transactionName=bar&transactionType=request&comparisonEnabled=true&offset=1d'
+      );
+    });
+  });
+});