Huge memory leak with Jest/Enzyme after upgrading to react-modal 3.X

Summary:

For a while now, I've been unable to upgrade to react-modal 3.X in my React 16 project with Jest/Enzyme because when I run tests Node itself actually crashes and I usually have to take some fairly nuclear steps such as force-quitting the process in my activity monitor app in order to use it again. The latest 2.X release of react-modal is totally fine.

Steps to reproduce:

1. Upgrade react-modal from 2.4.1 to 3.X
2. Run npm run jest
3. First few tests may run, but eventually the process hangs, and eventually these errors start to spill out:

<--- Last few GCs --->

[46548:0x102802400]    43615 ms: Mark-sweep 1402.9 (1437.6) -> 1402.9 (1436.6) MB, 1477.5 / 0.0 ms  (+ 0.0 ms in 0 steps since start of marking, biggest step 0.0 ms, walltime since start of marking 1477 ms) last resort GC in old space requested
[46548:0x102802400]    45072 ms: Mark-sweep 1402.9 (1436.6) -> 1402.9 (1436.6) MB, 1456.0 / 0.0 ms  last resort GC in old space requested


<--- JS stacktrace --->

==== JS stack trace =========================================

Security context: 0x38a049725ec1 <JSObject>
    1: read [/path/to/project/node_modules/react-dom/cjs/react-dom-server.node.development.js:~2206] [pc=0x181429965313](this=0x38a08a383211 <ReactDOMServerRenderer map = 0x38a00fd8cc29>,bytes=0x38a0125029a9 <Number inf>)
    3: renderToStaticMarkup [/path/to/project/node_modules/react-dom/cjs/react-dom-server.node.development.js:2512] [bytecode=0x38a0...

FATAL ERROR: CALL_AND_RETRY_LAST Allocation failed - JavaScript heap out of memory
 1: node::Abort() [/Users/username/.nvm/versions/node/v8.9.0/bin/node]
 2: node::FatalException(v8::Isolate*, v8::Local<v8::Value>, v8::Local<v8::Message>) [/Users/username/.nvm/versions/node/v8.9.0/bin/node]
 3: v8::internal::V8::FatalProcessOutOfMemory(char const*, bool) [/Users/username/.nvm/versions/node/v8.9.0/bin/node]
 4: v8::internal::Factory::NewFillerObject(int, bool, v8::internal::AllocationSpace) [/Users/username/.nvm/versions/node/v8.9.0/bin/node]
 5: v8::internal::Runtime_AllocateInTargetSpace(int, v8::internal::Object**, v8::internal::Isolate*) [/Users/username/.nvm/versions/node/v8.9.0/bin/node]
 6: 0x18142970463d

*Note that I've replaced the actual path and username in this snippet.