diff --git a/sdk/core/azure-core/src/test/java/com/azure/core/util/Base64UtilTests.java b/sdk/core/azure-core/src/test/java/com/azure/core/util/Base64UtilTests.java
new file mode 100644
index 000000000000..1e4f2926fb78
--- /dev/null
+++ b/sdk/core/azure-core/src/test/java/com/azure/core/util/Base64UtilTests.java
@@ -0,0 +1,51 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+package com.azure.core.util;
+
+import java.util.Arrays;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class Base64UtilTests {
+    @Test
+    public void testEncodeAndDecode() {
+        byte[] src = new byte[] { 65, 65, 69, 67, 65, 119, 81, 70, 66, 103, 99, 73, 67, 81 };
+        byte[] dst = Base64Util.encode(src);
+        assertTrue(Arrays.equals(Base64Util.decode(dst), src));
+    }
+
+    @Test
+    public void testEncodeNullValue() {
+        assertNull(Base64Util.encode(null));
+    }
+
+    @Test
+    public void testDecodeNullValue() {
+        assertNull(Base64Util.decode(null));
+    }
+
+    @Test
+    public void testDecodeString() {
+        byte[] src = new byte[] { 65, 65, 69, 67, 65, 119, 81, 70, 66, 103, 99, 73, 67, 81 };
+        String dstString = Base64Util.encodeToString(src);
+        assertTrue(Arrays.equals(Base64Util.decodeString(dstString), src));
+    }
+
+    @Test
+    public void testDecodeStringNullValue() {
+        assertNull(Base64Util.decodeString(null));
+    }
+
+    @Test
+    public void testEncodeURLWithoutPaddingNullValue() {
+        assertNull(Base64Util.encodeURLWithoutPadding(null));
+    }
+
+    @Test
+    public void testDecodeURLNullValue() {
+        assertNull(Base64Util.decodeURL(null));
+    }
+}
diff --git a/sdk/core/azure-core/src/test/java/com/azure/core/util/FluxUtilTest.java b/sdk/core/azure-core/src/test/java/com/azure/core/util/FluxUtilTest.java
index f354d1c5721d..0de295cabec6 100644
--- a/sdk/core/azure-core/src/test/java/com/azure/core/util/FluxUtilTest.java
+++ b/sdk/core/azure-core/src/test/java/com/azure/core/util/FluxUtilTest.java
@@ -9,9 +9,16 @@
 import com.azure.core.http.rest.Response;
 import com.azure.core.http.rest.SimpleResponse;
 import com.azure.core.util.logging.ClientLogger;
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
 import java.lang.reflect.Method;
 import java.lang.reflect.Type;
 import java.nio.ByteBuffer;
+import java.nio.channels.AsynchronousFileChannel;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.StandardOpenOption;
 import org.junit.jupiter.api.Test;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -120,6 +127,24 @@ public void testPageFluxError() {
             .verifyErrorMessage(errMsg);
     }
 
+    @Test
+    public void testWriteFile() throws Exception {
+        String toReplace = "test";
+        String original = "hello there";
+        String target = "testo there";
+
+        Flux<ByteBuffer> body = Flux.just(ByteBuffer.wrap(toReplace.getBytes(StandardCharsets.UTF_8)));
+        File file = createFileIfNotExist("target/test1");
+        FileOutputStream stream = new FileOutputStream(file);
+        stream.write(original.getBytes(StandardCharsets.UTF_8));
+        stream.close();
+        try (AsynchronousFileChannel channel = AsynchronousFileChannel.open(file.toPath(), StandardOpenOption.WRITE)) {
+            FluxUtil.writeFile(body, channel).block();
+            byte[] outputStream = Files.readAllBytes(file.toPath());
+            assertTrue(Arrays.equals(outputStream, target.getBytes(StandardCharsets.UTF_8)));
+        }
+    }
+
     public Flux<ByteBuffer> mockReturnType() {
         return Flux.just(ByteBuffer.wrap(new byte[0]));
     }
@@ -149,4 +174,13 @@ private Flux<String> serviceCallCollection(Context context) {
 
         return Flux.just(msg.split(" "));
     }
+
+    private File createFileIfNotExist(String fileName) throws IOException {
+        File file = new File(fileName);
+        if (file.getParentFile() != null) {
+            file.getParentFile().mkdirs();
+        }
+        file.createNewFile();
+        return file;
+    }
 }