polish: added test from work on v17 branch backported to v16

originally related to:

OverlappingFieldsCanBeMergedRule: Fix performance degradation (graphql#3958)

Co-authored-by: AaronMoat <AaronMoat@users.noreply.github.com>
Co-authored-by: Ivan Goncharov <ivan.goncharov.ua@gmail.com>

Author: 2 people

src/validation/__tests__/OverlappingFieldsCanBeMergedRule-test.ts

@@ -185,6 +185,24 @@ describe('Validate: Overlapping fields can be merged', () => {
     ]);
   });
 
+  it('different args, first has two, second missing one', () => {
+    expectErrors(`
+      fragment conflictingArgs on Dog {
+        doesKnowCommand(dogCommand: SIT, atExpertLevel: true)
+        doesKnowCommand(dogCommand: SIT)
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Fields "doesKnowCommand" conflict because they have differing arguments. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 3, column: 9 },
+          { line: 4, column: 9 },
+        ],
+      },
+    ]);
+  });
+
   it('conflicting arg values', () => {
     expectErrors(`
       fragment conflictingArgs on Dog {

src/validation/rules/OverlappingFieldsCanBeMergedRule.ts

@@ -680,11 +680,8 @@ function sameArguments(
     return false;
   }
 
-  /* c8 ignore next */
   if (args1.length !== args2.length) {
-    /* c8 ignore next */
     return false;
-    /* c8 ignore next */
   }
 
   const values2 = new Map(args2.map(({ name, value }) => [name.value, value]));