add test for questioned spec bug

src/execution/__tests__/questioned-spec-bug-test.ts

@@ -0,0 +1,90 @@
+import { describe, it } from 'mocha';
+
+import { expectJSON } from '../../__testUtils__/expectJSON.js';
+
+import { parse } from '../../language/parser.js';
+
+import type { GraphQLSchema } from '../../type/schema.js';
+
+import { validate } from '../../validation/validate.js';
+
+import { buildSchema } from '../../utilities/buildASTSchema.js';
+
+import { execute } from '../execute.js';
+
+async function executeQuery(args: {
+  schema: GraphQLSchema;
+  query: string;
+  rootValue?: unknown;
+}) {
+  const { schema, query, rootValue } = args;
+  const document = parse(query);
+  return execute({
+    schema,
+    document,
+    rootValue,
+  });
+}
+
+describe('Execute: default arguments', () => {
+  it('handles interfaces with fields with default arguments', async () => {
+    const schema = buildSchema(`
+      type Query {
+        someInterface: SomeInterface
+      }
+
+      interface SomeInterface {
+        echo(value: String! = "default"): String
+      }
+
+      type SomeType implements SomeInterface {
+        echo(value: String!): String
+      }
+    `);
+
+    const query = `
+      {
+        someInterface {
+          ... on SomeType {
+            echo
+          }
+          echo
+        }
+      }
+    `;
+
+    const rootValue = {
+      someInterface: {
+        __typename: 'SomeType',
+        echo: ({ value }: { value: string }) => value,
+      },
+    };
+
+    expectJSON(await executeQuery({ schema, query, rootValue })).toDeepEqual({
+      data: {
+        someInterface: {
+          echo: null,
+        },
+      },
+      errors: [
+        {
+          message:
+            'Argument "value" of required type "String!" was not provided.',
+          path: ['someInterface', 'echo'],
+          locations: [{ line: 5, column: 13 }],
+        },
+      ],
+    });
+
+    const errors = validate(schema, parse(query));
+
+    expectJSON(errors).toDeepEqual([
+      {
+        // This would pass validation for the interface, but we get a runtime error above.
+        message:
+          'Argument "SomeType.echo(value:)" of type "String!" is required, but it was not provided.',
+        locations: [{ line: 5, column: 13 }],
+      },
+    ]);
+  });
+});