add additional test case

src/type/__tests__/validation-test.ts

@@ -1996,7 +1996,7 @@ describe('Type System: Argument default values must be valid', () => {
     ]);
   });
 
-  it('Attempts to offer a suggested fix if possible', () => {
+  it('Attempts to offer a suggested fix if possible (programmatic)', () => {
     const Exotic = Symbol('Exotic');
 
     const testEnum = new GraphQLEnumType({
@@ -2060,6 +2060,83 @@ describe('Type System: Argument default values must be valid', () => {
       },
     ]);
   });
+
+  it('Attempts to offer a suggested fix if possible (SDL)', () => {
+    const originalSchema = buildSchema(`
+      enum TestEnum {
+        ONE
+        TWO
+      }
+
+      input TestInput {
+        self: TestInput
+        string: [String]!
+        enum: [TestEnum]
+      }
+
+      type Query {
+        field(
+          argWithPossibleFix: TestInput
+          argWithInvalidPossibleFix: TestInput
+          argWithoutPossibleFix: TestInput
+        ): Int
+      }
+    `);
+
+    const Exotic = Symbol('Exotic');
+
+    // workaround as we cannot inject custom internal values into enums defined in SDL
+    const testEnum = new GraphQLEnumType({
+      name: 'TestEnum',
+      values: {
+        ONE: { value: 1 },
+        TWO: { value: Exotic },
+      },
+    });
+
+    const testInput = assertInputObjectType(
+      originalSchema.getType('TestInput'),
+    );
+    testInput.getFields().enum.type = new GraphQLList(testEnum);
+
+    // workaround as we cannot inject exotic default values into arguments defined in SDL
+    const QueryType = assertObjectType(originalSchema.getType('Query'));
+    for (const arg of QueryType.getFields().field.args) {
+      arg.type = testInput;
+      switch (arg.name) {
+        case 'argWithPossibleFix':
+          arg.defaultValue = {
+            value: { self: null, string: [1], enum: Exotic },
+          };
+          break;
+        case 'argWithInvalidPossibleFix':
+          arg.defaultValue = { value: { string: null } };
+          break;
+        case 'argWithoutPossibleFix':
+          arg.defaultValue = { value: { enum: 'Exotic' } };
+          break;
+      }
+    }
+
+    expectJSON(validateSchema(originalSchema)).toDeepEqual([
+      {
+        message:
+          'Query.field(argWithPossibleFix:) has invalid default value: { self: null, string: [1], enum: Symbol(Exotic) }. Did you mean: { self: null, string: ["1"], enum: ["TWO"] }?',
+      },
+      {
+        message:
+          'Query.field(argWithInvalidPossibleFix:) has invalid default value at .string: Expected value of non-null type [String]! not to be null.',
+      },
+      {
+        message:
+          'Query.field(argWithoutPossibleFix:) has invalid default value: Expected value of type TestInput to include required field "string", found: { enum: "Exotic" }.',
+      },
+      {
+        message:
+          'Query.field(argWithoutPossibleFix:) has invalid default value at .enum: Value "Exotic" does not exist in "TestEnum" enum.',
+      },
+    ]);
+  });
 });
 
 describe('Type System: Input Object fields must have input types', () => {