diff --git a/commitlint/tests/testHelpers.ts b/commitlint/tests/testHelpers.ts
index c1809f76..e8d2f228 100644
--- a/commitlint/tests/testHelpers.ts
+++ b/commitlint/tests/testHelpers.ts
@@ -92,6 +92,12 @@ test("testing TypeHelpers.IsInstanceOf", () => {
 test("testing TypeHelpers.IsInstanceOf exceptions", () => {
     let strNull = null;
     expect(() => TypeHelpers.IsInstanceOf(strNull, String)).toThrowError("Invalid");
+    expect(() => TypeHelpers.IsInstanceOf(strNull, String)).toThrowError("parameter");
+    expect(() => TypeHelpers.IsInstanceOf(strNull, String)).toThrowError("null");
+    let strUndefined = undefined;
+    expect(() => TypeHelpers.IsInstanceOf(strUndefined, String)).toThrowError("Invalid");
+    expect(() => TypeHelpers.IsInstanceOf(strUndefined, String)).toThrowError("parameter");
+    expect(() => TypeHelpers.IsInstanceOf(strUndefined, String)).toThrowError("undefined");
 });
 
 export function runCommitLintOnMsg(inputMsg: string) {