test: add Node unit tests for toFormData and refactor buildURL to avoid param reassignment (#7272)

Co-authored-by: Jay <jasonsaayman@gmail.com>

test/unit/helpers/toFormData.js

@@ -0,0 +1,53 @@
+import assert from 'assert';
+import toFormData from '../../../lib/helpers/toFormData.js';
+import FormData from 'form-data';
+
+describe('helpers::toFormData', function () {
+  it('should convert a flat object to FormData', function () {
+    const data = {
+      foo: 'bar',
+      baz: 123
+    };
+
+    const formData = toFormData(data, new FormData());
+    
+    assert.ok(formData instanceof FormData);
+    // form-data package specific checks
+    assert.ok(formData._streams.length > 0);
+  });
+
+  it('should convert a nested object to FormData', function () {
+    const data = {
+      foo: {
+        bar: 'baz'
+      }
+    };
+
+    const formData = toFormData(data, new FormData());
+    
+    assert.ok(formData instanceof FormData);
+  });
+
+  it('should throw Error on circular reference', function () {
+    const data = {
+      foo: 'bar'
+    };
+    data.self = data;
+
+    try {
+      toFormData(data, new FormData());
+      assert.fail('Should have thrown an error');
+    } catch (e) {
+      assert.strictEqual(e.message, 'Circular reference detected in self');
+    }
+  });
+
+  it('should handle arrays', function () {
+    const data = {
+      arr: [1, 2, 3]
+    };
+
+    const formData = toFormData(data, new FormData());
+    assert.ok(formData instanceof FormData);
+  });
+});