diff --git a/src/isIsogram.test.js b/src/isIsogram.test.js
index dfb16184..c6fba4e6 100644
--- a/src/isIsogram.test.js
+++ b/src/isIsogram.test.js
@@ -6,4 +6,30 @@ describe('isIsogram', () => {
   it(`should be declared`, () => {
     expect(isIsogram).toBeInstanceOf(Function);
   });
+
+  it(`should return 'true' for an empty string`, () => {
+    const result = isIsogram('');
+
+    expect(result).toBeTruthy();
+  });
+
+  it(`should return 'true' for a word that has no repeated letters`, () => {
+    const result = isIsogram('playgrounds');
+
+    expect(result).toBeTruthy();
+  });
+
+  it(`should return 'false' for a word that has repeated letters`, () => {
+    const result = isIsogram('look');
+
+    expect(result).toBeFalsy();
+  });
+
+  it('should be case-insensitive', () => {
+    const result1 = isIsogram('Adam');
+    const result2 = isIsogram('Oops');
+
+    expect(result1).toBeFalsy();
+    expect(result2).toBeFalsy();
+  });
 });