test: move wtfnode invocation to signal handlers on main test runner

We had previously been running a `wtfnode` dump at the end of all
test runs as part of the client leak checker plugin. This is faulty
because it might catch false positive handles which are closing at
the time of test runner cleanup. If something is actually leaked,
it will now be caught at the time the test suite is cancelled
(either manually or in CI), and give better diagnostics about the
leaked handles.

Author: mbroadst

test/tools/runner/index.js

@@ -8,6 +8,7 @@ const parseConnectionString = require('../../../lib/core/uri_parser');
 const eachAsync = require('../../../lib/core/utils').eachAsync;
 const mock = require('mongodb-mock-server');
 const chalk = require('chalk');
+const wtfnode = require('wtfnode');
 
 const MONGODB_URI = process.env.MONGODB_URI || 'mongodb://localhost:27017';
 const filters = [];
@@ -107,3 +108,20 @@ chai.use(require('../../functional/spec-runner/matcher').default);
 chai.config.includeStack = true;
 chai.config.showDiff = true;
 chai.config.truncateThreshold = 0;
+
+// install signal handlers for printing open/active handles
+function dumpAndExit() {
+  // let other potential handlers run before exiting
+  process.nextTick(function() {
+    try {
+      wtfnode.dump();
+    } catch (e) {
+      console.log(e);
+    }
+
+    process.exit();
+  });
+}
+
+process.on('SIGINT', dumpAndExit);
+process.on('SIGTERM', dumpAndExit);

test/tools/runner/plugins/client_leak_checker.js

@@ -1,7 +1,6 @@
 'use strict';
 
 const TestConfiguration = require('../config');
-const wtfnode = require('wtfnode');
 const chalk = require('chalk');
 
 let activeClients = [];
@@ -31,8 +30,6 @@ function unifiedTopologyIsConnected(client) {
 }
 
 after(function() {
-  wtfnode.dump();
-
   const isUnifiedTopology = this.configuration.usingUnifiedTopology;
   const traces = [];
   const openClientCount = activeClients.reduce((count, client) => {
@@ -55,3 +52,4 @@ after(function() {
 
   activeClients = [];
 });
+