Add regression tests

Author: ahejlsberg

tests/cases/conformance/types/intersection/intersectionsAndEmptyObjects.ts

@@ -1,3 +1,5 @@
+// @target: es2015
+
 // Empty object type literals are removed from intersections types
 // that contain other object types
 
@@ -23,3 +25,54 @@ let x11: C & D;
 let x12: A & B & C & D;
 let x13: D & E;
 let x14: A & B & C & D & E;
+
+// Repro from #20225
+
+type Dictionary = { [name: string]: string };
+
+const intersectDictionaries = <F1 extends Dictionary, F2 extends Dictionary>(
+  d1: F1,
+  d2: F2,
+): F1 & F2 => Object.assign({}, d1, d2);
+
+const testDictionary = <T extends Dictionary>(_value: T) => { };
+
+const d1 = {};
+testDictionary(d1);
+const d2 = intersectDictionaries(d1, d1);
+testDictionary(d2);
+
+const d3 = {
+  s: '',
+};
+testDictionary(d3);
+const d4 = intersectDictionaries(d1, d3);
+testDictionary(d4);
+const d5 = intersectDictionaries(d3, d1);
+testDictionary(d5);
+const d6 = intersectDictionaries(d3, d3);
+testDictionary(d6);
+
+// Repro from #27044
+
+type choices<IChoiceList extends {
+    [key: string]: boolean;
+}> = IChoiceList & {
+    shoes:boolean;
+    food:boolean;
+};
+
+type IMyChoiceList = {
+    car: true
+};
+
+type IUnknownChoiceList = {};
+
+var defaultChoices: choices<{}>;
+var defaultChoicesAndEmpty: choices<{} & {}>;
+
+var myChoices: choices<IMyChoiceList>;
+var myChoicesAndEmpty: choices<IMyChoiceList & {}>;
+
+var unknownChoices: choices<IUnknownChoiceList>;
+var unknownChoicesAndEmpty: choices<IUnknownChoiceList & {}>;