diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index fbd677367..30649067a 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -40,6 +40,16 @@ jobs:
         run: yarn test
         working-directory: packages/mcp
 
+  ui:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - name: Run tests
+        run: yarn test
+        working-directory: packages/ui
+
   build:
     name: build (${{ matrix.package }}, ${{ matrix.variant }})
     timeout-minutes: 90
diff --git a/package.json b/package.json
index f26a4e00c..4f3757537 100644
--- a/package.json
+++ b/package.json
@@ -7,6 +7,7 @@
     "lint": "eslint",
     "format:write": "prettier --write \"**/*\"",
     "format:check": "prettier --check \"**/*\"",
+    "test:ui": "yarn --cwd ./packages/ui test",
     "type:check:api": "yarn --cwd ./packages/ui type:check:api",
     "dev:ui": "yarn --cwd ./packages/ui dev",
     "dev:api": "yarn --cwd ./packages/ui dev:api",
@@ -41,4 +42,4 @@
     "@changesets/cli": "^2.29.2",
     "@changesets/changelog-github": "^0.5.1"
   }
-}
+}
\ No newline at end of file
diff --git a/packages/ui/ava.config.js b/packages/ui/ava.config.js
new file mode 100644
index 000000000..756f31fe1
--- /dev/null
+++ b/packages/ui/ava.config.js
@@ -0,0 +1,6 @@
+module.exports = {
+  extensions: ['ts'],
+  require: ['./ts-node-register.cjs'],
+  timeout: '10m',
+  workerThreads: false,
+};
diff --git a/packages/ui/package.json b/packages/ui/package.json
index 0b90b9efd..1df072e86 100644
--- a/packages/ui/package.json
+++ b/packages/ui/package.json
@@ -9,9 +9,11 @@
     "dev": "node scripts/copy-versions.mjs && rollup -c -w",
     "dev:api": "ENV=dev deno task dev",
     "start": "sirv public",
-    "validate": "svelte-check"
+    "validate": "svelte-check",
+    "test": "ava"
   },
   "devDependencies": {
+    "ava": "^6.1.2",
     "@rollup/plugin-alias": "^5.0.0",
     "@rollup/plugin-commonjs": "^28.0.0",
     "@rollup/plugin-json": "^6.0.0",
@@ -38,6 +40,7 @@
     "svelte-preprocess": "^5.0.0",
     "tailwindcss": "^3.0.15",
     "tslib": "^2.0.0",
+    "ts-node": "^10.9.2",
     "typescript": "^5.0.0"
   },
   "dependencies": {
@@ -50,4 +53,4 @@
     "tippy.js": "^6.3.1",
     "util": "^0.12.4"
   }
-}
+}
\ No newline at end of file
diff --git a/packages/ui/src/solidity/remix.test.ts b/packages/ui/src/solidity/remix.test.ts
new file mode 100644
index 000000000..fce31fe7f
--- /dev/null
+++ b/packages/ui/src/solidity/remix.test.ts
@@ -0,0 +1,66 @@
+import test from 'ava';
+import { remixURL } from './remix';
+
+// Decoder used in Remix
+const decodeBase64 = (b64Payload: string) => {
+  const raw = atob(decodeURIComponent(b64Payload));
+  const bytes = Uint8Array.from(raw, c => c.charCodeAt(0));
+  return new TextDecoder().decode(bytes);
+};
+
+test('remixURL encodes code param decodable by decodeBase64', t => {
+  const contractSource = 'contract A{}';
+
+  const url = remixURL(contractSource);
+  const codeParam = url.searchParams.get('code');
+  t.truthy(codeParam, 'Expected code search param to be set');
+
+  const decoded = decodeBase64(codeParam!);
+  t.is(decoded, contractSource, 'Decoded code should equal original source');
+});
+
+test('remixURL sets deployProxy flag when upgradeable', t => {
+  const contractSource = 'contract A{}';
+
+  const urlTrue = remixURL(contractSource, true);
+  t.is(urlTrue.searchParams.get('deployProxy'), 'true');
+
+  const urlFalse = remixURL(contractSource, false);
+  t.is(urlFalse.searchParams.get('deployProxy'), null);
+});
+
+test('remixURL encodes code param with special characters decodable by decodeBase64', t => {
+  // not a valid contract
+  const contractSource = `// SPDX-License-Identifier: MIT
+// Compatible with OpenZeppelin Contracts ^5.4.0
+pragma solidity ^0.8.27;
+
+import {AccountERC7579} from "@openzeppelin/contracts/account/extensions/draft-AccountERC7579.sol";
+import {ERC7739} from "@openzeppelin/contracts/utils/cryptography/signers/draft-ERC7739.sol";
+
+contract MyAccount is ERC7739, AccountERC7579 {
+    constructor(address signer)
+        EIP712(unicode"MyAccount🌾", "1")
+        SignerECDSA(signer)
+    {}
+
+    function isValidSignature(bytes32 hash, bytes calldata signature)
+        public
+        view
+        override(AccountERC7579, ERC7739)
+        returns (bytes4)
+    {
+        // ERC-7739 can return the ERC-1271 magic value, 0xffffffff (invalid) or 0x77390001 (detection).
+        // If the returned value is 0xffffffff, fallback to ERC-7579 validation.
+        bytes4 erc7739magic = ERC7739.isValidSignature(hash, signature);
+        return erc7739magic == bytes4(0xffffffff) ? AccountERC7579.isValidSignature(hash, signature) : erc7739magic;
+    }
+}`;
+
+  const url = remixURL(contractSource);
+  const codeParam = url.searchParams.get('code');
+  t.truthy(codeParam, 'Expected code search param to be set');
+
+  const decoded = decodeBase64(codeParam!);
+  t.is(decoded, contractSource, 'Decoded code should equal original source');
+});
diff --git a/packages/ui/src/solidity/remix.ts b/packages/ui/src/solidity/remix.ts
index a4907e17b..e1d795bdf 100644
--- a/packages/ui/src/solidity/remix.ts
+++ b/packages/ui/src/solidity/remix.ts
@@ -1,11 +1,9 @@
 export function remixURL(code: string, upgradeable = false, overrideRemixURL?: string): URL {
   const remix = new URL(overrideRemixURL ?? 'https://remix.ethereum.org');
 
-  const codeWithEscapedSpecialCharacters = Array.from(new TextEncoder().encode(code), b => String.fromCharCode(b)).join(
-    '',
-  );
+  const encodedCode = btoa(String.fromCharCode(...new TextEncoder().encode(code))).replace(/=*$/, '');
 
-  remix.searchParams.set('code', btoa(codeWithEscapedSpecialCharacters).replace(/=*$/, ''));
+  remix.searchParams.set('code', encodedCode);
 
   if (upgradeable) {
     remix.searchParams.set('deployProxy', upgradeable.toString());
diff --git a/packages/ui/ts-node-register.cjs b/packages/ui/ts-node-register.cjs
new file mode 100644
index 000000000..14302dc81
--- /dev/null
+++ b/packages/ui/ts-node-register.cjs
@@ -0,0 +1,9 @@
+/* eslint-disable */
+
+// Configure ts-node to use a test-specific tsconfig
+const path = require('path');
+
+require('ts-node').register({
+  transpileOnly: true,
+  project: path.join(__dirname, 'tsconfig.test.json'),
+});
diff --git a/packages/ui/tsconfig.test.json b/packages/ui/tsconfig.test.json
new file mode 100644
index 000000000..23e4b49e6
--- /dev/null
+++ b/packages/ui/tsconfig.test.json
@@ -0,0 +1,17 @@
+{
+  "extends": "./tsconfig.json",
+  "compilerOptions": {
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "noEmit": true,
+    "lib": [
+      "es2020",
+      "dom",
+      "dom.iterable"
+    ]
+  },
+  "include": [
+    "src/**/*.ts"
+  ]
+}
+
diff --git a/yarn.lock b/yarn.lock
index 7dca4b0f8..aa364791b 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1523,7 +1523,7 @@ autoprefixer@^10.4.2:
     picocolors "^1.1.1"
     postcss-value-parser "^4.2.0"
 
-ava@^6.0.0:
+ava@^6.0.0, ava@^6.1.2:
   version "6.4.1"
   resolved "https://registry.yarnpkg.com/ava/-/ava-6.4.1.tgz#89ce905d73bcd6c1d55bbba2598df3dc74e957dd"
   integrity sha512-vxmPbi1gZx9zhAjHBgw81w/iEDKcrokeRk/fqDTyA2DQygZ0o+dUGRHFOtX8RA5N0heGJTTsIk7+xYxitDb61Q==
@@ -5936,7 +5936,7 @@ ts-interface-checker@^0.1.9:
   resolved "https://registry.yarnpkg.com/ts-interface-checker/-/ts-interface-checker-0.1.13.tgz#784fd3d679722bc103b1b4b8030bcddb5db2a699"
   integrity sha512-Y/arvbn+rrz3JCKl9C4kVNfTfSm2/mEp5FSz5EsZSANGPSlQrpRI5M4PKF+mJnE52jOO90PnPSc3Ur3bTQw0gA==
 
-ts-node@^10.4.0:
+ts-node@^10.4.0, ts-node@^10.9.2:
   version "10.9.2"
   resolved "https://registry.yarnpkg.com/ts-node/-/ts-node-10.9.2.tgz#70f021c9e185bccdca820e26dc413805c101c71f"
   integrity sha512-f0FFpIdcHgn8zcPSbf1dRevwt047YMnaiJM3u2w2RewrB+fob/zePZcrOyQoLMMO7aBIddLcQIEK5dYjkLnGrQ==