add adapter unit test

Author: baileympearson

test/unit/runtime_adapters.test.ts

@@ -0,0 +1,30 @@
+import { expect } from "chai"
+import { MongoClient, OsAdapter } from "../../src"
+import * as os from 'os';
+
+describe('Runtime Adapters tests', function () {
+    describe('`os`', function () {
+        describe('when no os adapter is provided', function () {
+            it(`defaults to Node's os module`, function () {
+                const client = new MongoClient('mongodb://localhost:27017');
+
+                expect(client.options.runtime.os).to.equal(os);
+            })
+        })
+
+        describe('when an os adapter is provided', function () {
+            it(`uses the user provided adapter`, function () {
+                const osAdapter: OsAdapter = {
+                    ...os
+                };
+                const client = new MongoClient('mongodb://localhost:27017', {
+                    runtimeAdapters: {
+                        os: osAdapter
+                    }
+                });
+
+                expect(client.options.runtime.os).to.equal(osAdapter);
+            })
+        })
+    })
+})