diff --git a/src/test/kotlin/filesystem/FSEntryTest.kt b/src/test/kotlin/filesystem/FSEntryTest.kt
new file mode 100644
index 0000000..b474ac2
--- /dev/null
+++ b/src/test/kotlin/filesystem/FSEntryTest.kt
@@ -0,0 +1,42 @@
+package filesystem
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class FSEntryTest {
+    @Test
+    fun `non-cyclic folder`() {
+        val folder =
+            FSFolder(
+                "folder",
+                listOf(
+                    FSFolder("folder", listOf()),
+                    FSFile("text.txt", "Hello!"),
+                ),
+            )
+        assertFalse(folder.isCyclic())
+    }
+
+    @Test
+    fun `cyclic folder`() {
+        val files = mutableListOf<FSEntry>()
+        val folder = FSFolder("folder", files)
+        files.add(folder)
+        assertTrue(folder.isCyclic())
+    }
+
+    @Test
+    fun `long cyclic folder`() {
+        val files = mutableListOf<FSEntry>()
+        val folder1 = FSFolder("folder", files)
+        val folder2 = FSFolder("folder2", listOf(folder1))
+        val folder3 = FSFolder("folder3", listOf(folder2))
+        val folder4 = FSFolder("folder4", listOf(folder3))
+        files.add(folder4)
+        assertTrue(folder1.isCyclic())
+        assertTrue(folder2.isCyclic())
+        assertTrue(folder3.isCyclic())
+        assertTrue(folder4.isCyclic())
+    }
+}
\ No newline at end of file