diff --git a/src/isIsogram.test.js b/src/isIsogram.test.js
index dfb16184..2e58e1e7 100644
--- a/src/isIsogram.test.js
+++ b/src/isIsogram.test.js
@@ -6,4 +6,20 @@ describe('isIsogram', () => {
   it(`should be declared`, () => {
     expect(isIsogram).toBeInstanceOf(Function);
   });
+
+  it('should return true for a word without repeating letters', () => {
+    expect(isIsogram('playgrounds')).toBe(true);
+  });
+
+  it('should return true for an empty string', () => {
+    expect(isIsogram('')).toBe(true);
+  });
+
+  it('should return false for a word with repeating letters', () => {
+    expect(isIsogram('look')).toBe(false);
+  });
+
+  it('should return false for repeating letters in different cases', () => {
+    expect(isIsogram('Adam')).toBe(false);
+  });
 });