diff --git a/hiero-enterprise-base/src/main/java/com/openelements/hiero/base/implementation/FileClientImpl.java b/hiero-enterprise-base/src/main/java/com/openelements/hiero/base/implementation/FileClientImpl.java
index 6f5c2fe2..cde3ff92 100644
--- a/hiero-enterprise-base/src/main/java/com/openelements/hiero/base/implementation/FileClientImpl.java
+++ b/hiero-enterprise-base/src/main/java/com/openelements/hiero/base/implementation/FileClientImpl.java
@@ -44,7 +44,7 @@ public FileId createFile(@NonNull final byte[] contents, @NonNull final Instant
 
     private FileId createFileImpl(@NonNull final byte[] contents, @Nullable final Instant expirationTime)
             throws HieroException {
-        Objects.requireNonNull(contents, "fileId must not be null");
+        Objects.requireNonNull(contents, "contents must not be null");
         if (contents.length > FileCreateRequest.FILE_MAX_SIZE) {
             throw new HieroException("File contents must be less than " + FileCreateRequest.FILE_MAX_SIZE + " bytes");
         }
diff --git a/hiero-enterprise-base/src/test/java/com/openelements/hiero/base/test/FileClientImplTest.java b/hiero-enterprise-base/src/test/java/com/openelements/hiero/base/test/FileClientImplTest.java
index 16afc7c1..a8ba70bf 100644
--- a/hiero-enterprise-base/src/test/java/com/openelements/hiero/base/test/FileClientImplTest.java
+++ b/hiero-enterprise-base/src/test/java/com/openelements/hiero/base/test/FileClientImplTest.java
@@ -3,6 +3,10 @@
 import com.hedera.hashgraph.sdk.FileId;
 import com.openelements.hiero.base.HieroException;
 import com.openelements.hiero.base.implementation.FileClientImpl;
+import com.openelements.hiero.base.protocol.FileCreateResult;
+import com.openelements.hiero.base.protocol.FileCreateRequest;
+import com.openelements.hiero.base.protocol.FileAppendRequest;
+import com.openelements.hiero.base.protocol.FileAppendResult;
 import com.openelements.hiero.base.protocol.FileInfoRequest;
 import com.openelements.hiero.base.protocol.FileInfoResponse;
 import com.openelements.hiero.base.protocol.ProtocolLayerClient;
@@ -11,8 +15,12 @@
 import org.junit.jupiter.api.Test;
 import org.mockito.Mockito;
 
+import java.time.Instant;
+
 import static org.mockito.ArgumentMatchers.any;
-import static org.mockito.Mockito.*;
+import static org.mockito.Mockito.when;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.times;
 
 public class FileClientImplTest {
     ProtocolLayerClient protocolLayerClient;
@@ -24,6 +32,94 @@ void setup() {
         fileClientImpl = new FileClientImpl(protocolLayerClient);
     }
 
+    @Test
+    void testCreateFile() throws HieroException {
+        // mock
+        final FileId fileId = FileId.fromString("1.2.3");
+        final FileCreateResult fileCreateResult = Mockito.mock(FileCreateResult.class);
+
+        // given
+        final byte[] content = "Hello Hiero!".getBytes();
+
+        //then
+        when(protocolLayerClient.executeFileCreateTransaction(any(FileCreateRequest.class)))
+                .thenReturn(fileCreateResult);
+        when(fileCreateResult.fileId()).thenReturn(fileId);
+
+        final FileId result = fileClientImpl.createFile(content);
+
+        verify(protocolLayerClient, times(1))
+                .executeFileCreateTransaction(any(FileCreateRequest.class));
+        verify(fileCreateResult, times(1)).fileId();
+        Assertions.assertEquals(fileId, result);
+    }
+
+    @Test
+    void testCreateFileForSizeGreaterThanFileCreateMaxSize() throws HieroException {
+        // mock
+        final FileId fileId = FileId.fromString("1.2.3");
+        final FileCreateResult fileCreateResult = Mockito.mock(FileCreateResult.class);
+        final FileAppendResult fileAppendResult = Mockito.mock(FileAppendResult.class);
+
+        // given
+        final byte[] content = new byte[FileCreateRequest.FILE_CREATE_MAX_SIZE * 2];
+        // -1 because 1 for executeFileCreateTransaction()
+        final int appendCount = Math.floorDiv(content.length, FileCreateRequest.FILE_CREATE_MAX_SIZE) - 1;
+
+        //then
+        when(protocolLayerClient.executeFileCreateTransaction(any(FileCreateRequest.class)))
+                .thenReturn(fileCreateResult);
+        when(fileCreateResult.fileId()).thenReturn(fileId);
+        when(protocolLayerClient.executeFileAppendRequestTransaction(any(FileAppendRequest.class)))
+                .thenReturn(fileAppendResult);
+
+        final FileId result = fileClientImpl.createFile(content);
+
+        verify(protocolLayerClient, times(1))
+                .executeFileCreateTransaction(any(FileCreateRequest.class));
+        verify(fileCreateResult, times(1)).fileId();
+        verify(protocolLayerClient, times(appendCount))
+                .executeFileAppendRequestTransaction(any(FileAppendRequest.class));
+        Assertions.assertEquals(fileId, result);
+    }
+
+    @Test
+    void testCreateFileThrowsExceptionForSizeGreaterThanMaxFileSize() {
+        final String message = "File contents must be less than " + FileCreateRequest.FILE_MAX_SIZE + " bytes";
+        // given
+        final byte[] contents = new byte[FileCreateRequest.FILE_MAX_SIZE + 1];
+
+        // then
+        final HieroException exception = Assertions.assertThrows(
+                HieroException.class, () -> fileClientImpl.createFile(contents)
+        );
+        Assertions.assertTrue(exception.getMessage().contains(message));
+    }
+
+    @Test
+    void testCreateFileThrowsExceptionForExpirationTimeBeforeNow() {
+        final String message = "Expiration time must be in the future";
+        // given
+        final byte[] contents = "Hello Hiero!".getBytes();
+        final Instant expiration = Instant.now().minusSeconds(1);
+
+        // then
+        final IllegalArgumentException exception =Assertions.assertThrows(
+                IllegalArgumentException.class, () -> fileClientImpl.createFile(contents, expiration)
+        );
+        Assertions.assertTrue(exception.getMessage().contains(message));
+    }
+
+    @Test
+    void testCreateFileThrowsExceptionForNullContent() {
+        final String message = "contents must not be null";
+
+        final NullPointerException exception = Assertions.assertThrows(
+                NullPointerException.class, () -> fileClientImpl.createFile(null)
+        );
+        Assertions.assertTrue(exception.getMessage().contains(message));
+    }
+
     @Test
     void testGetFileSize() throws HieroException {
         // mocks
@@ -60,6 +156,11 @@ void testGetFileSizeThrowsExceptionForInvalidId() throws HieroException {
 
     @Test
     void testGetFileSizeThrowsExceptionForNullId() {
-        Assertions.assertThrows(NullPointerException.class, () -> fileClientImpl.getSize(null));
+        final String message = "fileId must not be null";
+
+        final NullPointerException exception = Assertions.assertThrows(
+                NullPointerException.class, () -> fileClientImpl.getSize(null)
+        );
+        Assertions.assertTrue(exception.getMessage().contains(message));
     }
 }
diff --git a/hiero-enterprise-spring/src/test/java/com/openelements/hiero/spring/test/FileClientTests.java b/hiero-enterprise-spring/src/test/java/com/openelements/hiero/spring/test/FileClientTests.java
index aa2b0d13..84bcb429 100644
--- a/hiero-enterprise-spring/src/test/java/com/openelements/hiero/spring/test/FileClientTests.java
+++ b/hiero-enterprise-spring/src/test/java/com/openelements/hiero/spring/test/FileClientTests.java
@@ -7,6 +7,8 @@
 import java.time.Instant;
 import java.time.temporal.ChronoUnit;
 import java.util.stream.IntStream;
+
+import com.openelements.hiero.base.protocol.FileCreateRequest;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
@@ -45,7 +47,7 @@ void testCreateEmptyFile() throws Exception {
     @Test
     void testCreateSmallFile() throws Exception {
         //given
-        final byte[] contents = "Hello, Hedera!".getBytes();
+        final byte[] contents = "Hello, Hiero!".getBytes();
 
         //when
         final FileId fileId = fileClient.createFile(contents);
@@ -57,7 +59,7 @@ void testCreateSmallFile() throws Exception {
     @Test
     void testCreateLargeFile() throws Exception {
         //given
-        final byte[] contents = IntStream.range(0, 500).mapToObj(i -> "Hello, Hedera!")
+        final byte[] contents = IntStream.range(0, 500).mapToObj(i -> "Hello, Hiero!")
                 .reduce((a, b) -> a + b)
                 .get()
                 .getBytes();
@@ -69,6 +71,27 @@ void testCreateLargeFile() throws Exception {
         Assertions.assertNotNull(fileId);
     }
 
+    @Test
+    void testCreateFileThrowExceptionIfExceedMaxFileSize() {
+        // given
+        final byte[] contents = new byte[FileCreateRequest.FILE_MAX_SIZE + 1];
+
+        // then
+        Assertions.assertThrows(HieroException.class, () -> fileClient.createFile(contents));
+    }
+
+    @Test
+    void testCreateFileThrowExceptionIfExpirationTimeBeforeNow() {
+        // given
+        final byte[] contents = "Hello Hiero!".getBytes();
+        final Instant definedExpirationTime = Instant.now().minusSeconds(60);
+
+        // then
+        Assertions.assertThrows(
+                IllegalArgumentException.class, () -> fileClient.createFile(contents, definedExpirationTime)
+        );
+    }
+
     @Test
     void testReadFileByFileId() throws Exception {
         //given