Added tests.

tests/cases/compiler/errorsOnUnionsOfOverlappingObjects01.ts

@@ -0,0 +1,29 @@
+interface Foo {
+    a: string;
+    b: number;
+};
+
+interface Bar {
+    b: string;
+}
+
+interface Other {
+    totallyUnrelatedProperty: number;
+}
+
+export let x = { a: '', b: '' };
+
+declare function f(x: Foo | Other): any;
+
+f(x);
+f({ a: '', b: '' })
+
+declare function g(x: Bar | Other): any;
+
+g(x);
+g({ a: '', b: '' })
+
+declare function h(x: Foo | Bar | Other): any;
+
+h(x);
+h({ a: '', b: '' })