diff --git a/tests/cases/compiler/duplicateIdentifiersAcrossFileBoundaries.ts b/tests/cases/compiler/duplicateIdentifiersAcrossFileBoundaries.ts
new file mode 100644
index 00000000000..94e5cd94ab1
--- /dev/null
+++ b/tests/cases/compiler/duplicateIdentifiersAcrossFileBoundaries.ts
@@ -0,0 +1,33 @@
+// @declaration: true
+
+// @Filename: file1.ts
+interface I { }
+class C1 { }
+class C2 { }
+function f() { }
+var v = 3;
+
+class Foo {
+    static x: number;
+}
+
+module N {
+    export module F {
+        var t;
+    }
+}
+
+// @Filename: file2.ts
+class I { } // error -- cannot merge interface with non-ambient class
+interface C1 { } // error -- cannot merge interface with non-ambient class
+function C2() { } // error -- cannot merge function with non-ambient class
+class f { } // error -- cannot merge function with non-ambient class
+var v = 3;
+
+module Foo {
+    export var x: number; // error for redeclaring var in a different parent
+}
+
+declare module N {
+    export function F(); // no error because function is ambient
+}
diff --git a/tests/cases/conformance/classes/classDeclarations/classAndInterfaceMerge.d.ts b/tests/cases/conformance/classes/classDeclarations/classAndInterfaceMerge.d.ts
new file mode 100644
index 00000000000..1ef7724f81d
--- /dev/null
+++ b/tests/cases/conformance/classes/classDeclarations/classAndInterfaceMerge.d.ts
@@ -0,0 +1,25 @@
+
+interface C { }
+
+declare class C { }
+
+interface C { }
+
+interface C { }
+
+declare module M {
+
+    interface C1 { }
+
+    class C1 { }
+
+    interface C1 { }
+
+    interface C1 { }
+
+    export class C2 { }
+}
+
+declare module M {
+    export interface C2 { }
+}
\ No newline at end of file
diff --git a/tests/cases/conformance/classes/classDeclarations/declaredClassMergedwithSelf.ts b/tests/cases/conformance/classes/classDeclarations/declaredClassMergedwithSelf.ts
index 4688fec9e26..7445104e228 100644
--- a/tests/cases/conformance/classes/classDeclarations/declaredClassMergedwithSelf.ts
+++ b/tests/cases/conformance/classes/classDeclarations/declaredClassMergedwithSelf.ts
@@ -1,3 +1,6 @@
+
+// @Filename: file1.ts
+
 declare class C1 {}
 
 declare class C1 {}
@@ -6,4 +9,12 @@ declare class C2 {}
 
 interface C2 {}
 
-declare class C2 {}
\ No newline at end of file
+declare class C2 {}
+
+// @Filename: file2.ts
+
+declare class C3 { }
+
+// @Filename: file3.ts
+
+declare class C3 { }
\ No newline at end of file
diff --git a/tests/cases/conformance/classes/classDeclarations/mergedClassInterface.ts b/tests/cases/conformance/classes/classDeclarations/mergedClassInterface.ts
index 4fac95b516a..29400c63808 100644
--- a/tests/cases/conformance/classes/classDeclarations/mergedClassInterface.ts
+++ b/tests/cases/conformance/classes/classDeclarations/mergedClassInterface.ts
@@ -1,11 +1,54 @@
-declare class C1 {}
+// @declaration: true
 
-interface C1 {}
+// @Filename: file1.ts
 
-interface C2 {}
+declare class C1 { }
 
-declare class C2 {}
+interface C1 { }
 
-interface C2 {}
+interface C2 { }
 
-interface C2 {}
\ No newline at end of file
+declare class C2 { }
+
+class C3 { } // error -- cannot merge non-ambient class and interface
+
+interface C3 { } // error -- cannot merge non-ambient class and interface
+
+interface C4 { } // error -- cannot merge non-ambient class and interface
+
+class C4 { } // error -- cannot merge non-ambient class and interface
+
+interface C5 {
+    x1: number;
+}
+
+declare class C5 {
+    x2: number;
+}
+
+interface C5 {
+    x3: number;
+}
+
+interface C5 {
+    x4: number;
+}
+
+// checks if properties actually were merged
+var c5 : C5;
+c5.x1;
+c5.x2;
+c5.x3;
+c5.x4;
+
+// @Filename: file2.ts
+
+declare class C6 { }
+
+interface C7 { }
+
+// @Filename: file3.ts
+
+interface C6 { }
+
+declare class C7 { }
\ No newline at end of file