Add tests for #15358 (#17664)

tests/baselines/reference/checkTypePredicateForRedundantProperties.errors.txt

@@ -0,0 +1,13 @@
+tests/cases/compiler/checkTypePredicateForRedundantProperties.ts(1,35): error TS2300: Duplicate identifier 'a'.
+tests/cases/compiler/checkTypePredicateForRedundantProperties.ts(1,46): error TS2300: Duplicate identifier 'a'.
+
+
+==== tests/cases/compiler/checkTypePredicateForRedundantProperties.ts (2 errors) ====
+    function addProp2(x: any): x is { a: string; a: string; } {
+                                      ~
+!!! error TS2300: Duplicate identifier 'a'.
+                                                 ~
+!!! error TS2300: Duplicate identifier 'a'.
+        return true;
+    }
+    

tests/baselines/reference/checkTypePredicateForRedundantProperties.js

@@ -0,0 +1,10 @@
+//// [checkTypePredicateForRedundantProperties.ts]
+function addProp2(x: any): x is { a: string; a: string; } {
+    return true;
+}
+
+
+//// [checkTypePredicateForRedundantProperties.js]
+function addProp2(x) {
+    return true;
+}

tests/cases/compiler/checkTypePredicateForRedundantProperties.ts

@@ -0,0 +1,3 @@
+function addProp2(x: any): x is { a: string; a: string; } {
+    return true;
+}