Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/test/helpers/customError.js

@@ -0,0 +1,24 @@
+const { config } = require('hardhat');
+
+const optimizationsEnabled = config.solidity.compilers.some(c => c.settings.optimizer.enabled);
+
+/** Revert handler that supports custom errors. */
+async function expectRevertCustomError(promise, reason) {
+  try {
+    await promise;
+    expect.fail("Expected promise to throw but it didn't");
+  } catch (revert) {
+    if (reason) {
+      if (optimizationsEnabled) {
+        // Optimizations currently mess with Hardhat's decoding of custom errors
+        expect(revert.message).to.include.oneOf([reason, 'unrecognized return data or custom error']);
+      } else {
+        expect(revert.message).to.include(reason);
+      }
+    }
+  }
+}
+
+module.exports = {
+  expectRevertCustomError,
+};