feat(esm): Add test case for esm imports.

Context:
sveltejs/kit#612
nodejs/node#27408

.github/workflows/ci_main.yml

@@ -38,4 +38,7 @@ jobs:
     - name: import
       if: ${{ matrix.node == '14' }}
       run: npm run test:import
+    - name: import
+      if: ${{ matrix.node == '14' || matrix.node == '15' }}
+      run: npm run test:esm
 

package.json

@@ -57,6 +57,7 @@
     "prepublishOnly": "npm run build:package && npm run lint && npm run test && npm run test:circular && npm run dtslint && npm run test:side-effects && npm run api_guardian",
     "publish_docs": "./publish_docs.sh",
     "test": "npm run compile && mocha --config spec/support/.mocharc.js \"dist/spec/**/*-spec.js\"",
+    "test:esm": "node spec/module-test-spec.mjs",
     "test:browser": "echo \"Browser test is not working currently\" && exit -1 && npm-run-all build:spec:browser && opn spec/support/mocha-browser-runner.html",
     "test:circular": "dependency-cruiser --validate .dependency-cruiser.json -x \"^node_modules\" dist/esm5",
     "test:systemjs": "node integration/systemjs/systemjs-compatibility-spec.js",

spec/module-test-spec.mjs

@@ -0,0 +1,13 @@
+/* Test file to ensure rxjs can be loaded from esm
+
+https://github.com/ReactiveX/rxjs/pull/6192
+If this fails node will error when running this with an error like
+node:internal/process/esm_loader:74
+    internalBinding('errors').triggerUncaughtException(
+*/
+import {Observable} from 'rxjs';
+import * as o from 'rxjs/operators';
+import * as a from 'rxjs/ajax';
+import * as f from 'rxjs/fetch';
+import * as t from 'rxjs/testing';
+import * as w from 'rxjs/webSocket';