Add test for keepAlive+maxSockets when using https

packages/agent-base/test/test.ts

@@ -568,5 +568,63 @@ describe('Agent (TypeScript)', () => {
 				server.close();
 			}
 		});
+
+		it('should support `keepAlive: true` with `maxSockets`', async () => {
+			let reqCount = 0;
+			let connectCount = 0;
+
+			class MyAgent extends Agent {
+				async connect(
+					_req: http.ClientRequest,
+					opts: AgentConnectOpts
+				) {
+					connectCount++;
+					assert(opts.secureEndpoint === true);
+					await sleep(10);
+					return tls.connect(opts);
+				}
+			}
+			const agent = new MyAgent({ keepAlive: true, maxSockets: 1 });
+
+			const server = https.createServer(sslOptions, async (req, res) => {
+				expect(req.headers.connection).toEqual('keep-alive');
+				reqCount++;
+				await sleep(10);
+				res.end();
+			});
+			const addr = await listen(server);
+
+			try {
+				const resPromise = req(new URL('/foo', addr), {
+					agent,
+					rejectUnauthorized: false,
+				});
+				const res2Promise = req(new URL('/another', addr), {
+					agent,
+					rejectUnauthorized: false,
+				});
+
+				const res = await resPromise;
+				expect(reqCount).toEqual(1);
+				expect(connectCount).toEqual(1);
+				expect(res.headers.connection).toEqual('keep-alive');
+
+				res.resume();
+				const s1 = res.socket;
+				await once(s1, 'free');
+
+				const res2 = await res2Promise;
+				expect(reqCount).toEqual(2);
+				expect(connectCount).toEqual(1);
+				expect(res2.headers.connection).toEqual('keep-alive');
+				assert(res2.socket === s1);
+
+				res2.resume();
+				await once(res2.socket, 'free');
+			} finally {
+				agent.destroy();
+				server.close();
+			}
+		});
 	});
 });