Add fourslash testcases

tests/cases/fourslash/getSemanticDiagnosticForDeclaration.ts

@@ -0,0 +1,10 @@
+/// <reference path="fourslash.ts" />
+
+// @declaration: true
+//// interface privateInterface {}
+//// export class Bar implements /*1*/privateInterface/*2*/{ }
+
+verify.errorExistsBetweenMarkers("1", "2");
+verify.numberOfErrorsInCurrentFile(1);
+
+

tests/cases/fourslash/getSemanticDiagnosticForNoDeclaration.ts

@@ -0,0 +1,9 @@
+/// <reference path="fourslash.ts" />
+
+//// interface privateInterface {}
+//// export class Bar implements /*1*/privateInterface/*2*/{ }
+
+debugger
+verify.numberOfErrorsInCurrentFile(0);
+
+