Reorganize the repo structure (#2503)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

test/migrate-imports.test.js

@@ -0,0 +1,25 @@
+const path = require('path');
+const { promises: fs, constants: { F_OK } } = require('fs');
+const { expect } = require('chai');
+
+const { pathUpdates, updateImportPaths } = require('../scripts/migrate-imports.js');
+
+describe('migrate-imports.js', function () {
+  it('every new path exists', async function () {
+    for (const p of Object.values(pathUpdates)) {
+      await fs.access(path.join('contracts', p), F_OK);
+    }
+  });
+
+  it('replaces import paths in a file', async function () {
+    const source = `
+import '@openzeppelin/contracts/math/Math.sol';
+import '@openzeppelin/contracts-upgradeable/math/MathUpgradeable.sol';
+    `;
+    const expected = `
+import '@openzeppelin/contracts/utils/math/Math.sol';
+import '@openzeppelin/contracts-upgradeable/utils/math/MathUpgradeable.sol';
+    `;
+    expect(updateImportPaths(source)).to.equal(expected);
+  });
+});