diff --git a/src/main/kotlin/filesystem/FSCreator.kt b/src/main/kotlin/filesystem/FSCreator.kt
index 84b4487..cda4e58 100644
--- a/src/main/kotlin/filesystem/FSCreator.kt
+++ b/src/main/kotlin/filesystem/FSCreator.kt
@@ -53,4 +53,5 @@ class FSCreator {
 }
 
 class CyclicFolderException : Exception("Cyclic FSFolders are not supported")
+
 class DuplicateEntryNameException : Exception("Folder contains entries with duplicate names")
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diff --git a/src/test/kotlin/filesystem/FSCreatorTest.kt b/src/test/kotlin/filesystem/FSCreatorTest.kt
index 77c20fd..9d19bca 100644
--- a/src/test/kotlin/filesystem/FSCreatorTest.kt
+++ b/src/test/kotlin/filesystem/FSCreatorTest.kt
@@ -104,7 +104,7 @@ class FSCreatorTest {
                     "folder",
                     listOf(
                         FSFolder(
-                            "folder",
+                            "folder", // Repeated name should be fine here (not throw)
                             listOf(
                                 FSFolder(
                                     "secrets",
@@ -152,4 +152,34 @@ class FSCreatorTest {
             creator.create(folder4, "_tmp")
         }
     }
+
+    @Test
+    fun `create throws on folder with duplicate names`() {
+        val folder =
+            FSFolder(
+                "folder",
+                listOf(
+                    FSFile("README.md", "# Test File"),
+                    FSFile("hello-world.txt", "Hello World!"),
+                    FSFolder(
+                        "src",
+                        listOf(
+                            FSFile("README.md", "# Source files"),
+                            FSFolder(
+                                "solution",
+                                listOf(
+                                    FSFile("solution.py", "print('1 + 1 = 1')"),
+                                    FSFile("tmp", "A temporary file"),
+                                    FSFolder("tmp", listOf()),
+                                ),
+                            ),
+                        ),
+                    ),
+                    FSFolder("tmp", listOf()),
+                ),
+            )
+        assertThrows<DuplicateEntryNameException> {
+            creator.create(folder, "_tmp")
+        }
+    }
 }
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diff --git a/src/test/kotlin/filesystem/FSEntryTest.kt b/src/test/kotlin/filesystem/FSEntryTest.kt
index b474ac2..86076bd 100644
--- a/src/test/kotlin/filesystem/FSEntryTest.kt
+++ b/src/test/kotlin/filesystem/FSEntryTest.kt
@@ -1,10 +1,34 @@
 package filesystem
 
-import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.*
 import kotlin.test.assertFalse
 import kotlin.test.assertTrue
 
 class FSEntryTest {
+    @Test
+    fun `valid name entries`() {
+        assertDoesNotThrow("should construct FSFile and FSFolder without throwing") {
+            FSFile("A file with a name.tar.xz", "Contents")
+            FSFolder(".a folder with a name", listOf())
+        }
+    }
+
+    @Test
+    fun `invalid name entries`() {
+        assertThrows<InvalidEntryNameException> {
+            FSFile("File/here", "Contents")
+        }
+        assertThrows<InvalidEntryNameException> {
+            FSFolder("Folder/here", listOf())
+        }
+        assertThrows<InvalidEntryNameException> {
+            FSFolder(".", listOf())
+        }
+        assertThrows<InvalidEntryNameException> {
+            FSFolder("/", listOf())
+        }
+    }
+
     @Test
     fun `non-cyclic folder`() {
         val folder =
@@ -39,4 +63,74 @@ class FSEntryTest {
         assertTrue(folder3.isCyclic())
         assertTrue(folder4.isCyclic())
     }
+
+    @Test
+    fun `no duplicate names folder`() {
+        val folder =
+            FSFolder(
+                "folder",
+                listOf(
+                    FSFile("README.md", "# Test File"),
+                    FSFile("hello-world.txt", "Hello World!"),
+                    FSFolder(
+                        "src",
+                        listOf(
+                            FSFile("README.md", "# Source files"),
+                            FSFile("solution-1.py", "print('1 + 1 = 1')"),
+                            FSFile("solution-2.py", "print('1 + 1 = 1')"),
+                        ),
+                    ),
+                    FSFolder("tmp", listOf()),
+                ),
+            )
+        assertFalse(folder.hasDuplicateNames())
+        assertFalse(folder.deepHasDuplicateNames())
+    }
+
+    @Test
+    fun `shallow duplicate names folder`() {
+        val folder =
+            FSFolder(
+                "folder",
+                listOf(
+                    FSFile("README.md", "# Test File"),
+                    FSFile("hello-world.txt", "Hello World!"),
+                    FSFolder(
+                        "src",
+                        listOf(
+                            FSFile("README.md", "# Source files"),
+                            FSFile("solution-1.py", "print('1 + 1 = 1')"),
+                            FSFile("solution-2.py", "print('1 + 1 = 1')"),
+                        ),
+                    ),
+                    FSFolder("tmp", listOf()),
+                    FSFile("tmp", "A temporary file"),
+                ),
+            )
+        assertTrue(folder.hasDuplicateNames())
+        assertTrue(folder.deepHasDuplicateNames())
+    }
+
+    @Test
+    fun `deep duplicate names folder`() {
+        val folder =
+            FSFolder(
+                "folder",
+                listOf(
+                    FSFile("README.md", "# Test File"),
+                    FSFile("hello-world.txt", "Hello World!"),
+                    FSFolder(
+                        "src",
+                        listOf(
+                            FSFile("README.md", "# Source files"),
+                            FSFile("solution-1.py", "print('1 + 1 = 1')"),
+                            FSFile("solution-1.py", "print('1 + 1 = 1')"),
+                        ),
+                    ),
+                    FSFolder("tmp", listOf()),
+                ),
+            )
+        assertFalse(folder.hasDuplicateNames())
+        assertTrue(folder.deepHasDuplicateNames())
+    }
 }
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