fix mysql2 test failure resulting from attempting to mix dynamic-import, require, and coping with on-the-fly .ts->.js translation for the test run

Author: trentm

plugins/node/opentelemetry-instrumentation-mysql2/test/mysql.test.ts

@@ -1240,12 +1240,28 @@ describe('mysql2', () => {
         }
       });
 
-      const { MySQL2Instrumentation } = await import('../src/index.js');
+      // Here we want to dynamically load the instrumentation.
+      // - `await import('../src')` does not work with tsconfig `moduleResolution: "node16"`
+      //   because relative imports must use a suffix
+      // - `await import('../src/index.js')` does not work because when running
+      //   the test files from "./test/", instead of from "./build/test/", there
+      //   *isn't* a "index.js" file at that relative path.
+      // - `await import('../build/src/index.js')` does not work because that
+      //   is a different module, hence mismatched `MySQL2Instrumentation` types.
+      // We fallback to using `require`. This is what the emitted JS used when
+      // tsconfig was target=ES2017,module=commonjs. It also matches the
+      // `require.cache` deletions above.
+      //
+      // (IMO, a better solution for a clean test of `mysql2/promise` would
+      // be to use out-of-process testing as provided by `runTestFixture` in
+      // contrib-test-utils.)
+      const { MySQL2Instrumentation } = require('../src');
       instrumentation = new MySQL2Instrumentation();
       instrumentation.enable();
       instrumentation.disable();
 
-      createConnection = (await import('mysql2/promise')).createConnection;
+      // createConnection = (await import('mysql2/promise')).createConnection;
+      createConnection = require('mysql2/promise').createConnection;
 
       if (!shouldTest) {
         // this.skip() workaround