diff --git a/core-java/src/main/resources/countries.properties b/core-java/src/main/resources/countries.properties
new file mode 100644
index 0000000000..3c1f53aded
--- /dev/null
+++ b/core-java/src/main/resources/countries.properties
@@ -0,0 +1,3 @@
+UK
+US
+Germany
diff --git a/core-java/src/test/java/com/baeldung/file/FileOutputStreamTest.java b/core-java/src/test/java/com/baeldung/file/FileOutputStreamTest.java
index 98984f9781..451c1b4c4d 100644
--- a/core-java/src/test/java/com/baeldung/file/FileOutputStreamTest.java
+++ b/core-java/src/test/java/com/baeldung/file/FileOutputStreamTest.java
@@ -14,7 +14,7 @@ import com.baeldung.util.StreamUtils;
 
 public class FileOutputStreamTest {
 
-    public static final String fileName = "src/main/resources/countries.txt";
+    public static final String fileName = "src/main/resources/countries.properties";
 
     @Test
     public void whenAppendToFileUsingFileOutputStream_thenCorrect() throws Exception {
diff --git a/core-java/src/test/java/com/baeldung/file/FileUtilsTest.java b/core-java/src/test/java/com/baeldung/file/FileUtilsTest.java
index aae3c9fa1f..9ee8726575 100644
--- a/core-java/src/test/java/com/baeldung/file/FileUtilsTest.java
+++ b/core-java/src/test/java/com/baeldung/file/FileUtilsTest.java
@@ -16,7 +16,7 @@ import com.baeldung.util.StreamUtils;
 
 public class FileUtilsTest {
 
-    public static final String fileName = "src/main/resources/countries.txt";
+    public static final String fileName = "src/main/resources/countries.properties";
 
     @Test
     public void whenAppendToFileUsingFiles_thenCorrect() throws IOException {
diff --git a/core-java/src/test/java/com/baeldung/file/FileWriterTest.java b/core-java/src/test/java/com/baeldung/file/FileWriterTest.java
index b916f2b2c1..8d2ce4310e 100644
--- a/core-java/src/test/java/com/baeldung/file/FileWriterTest.java
+++ b/core-java/src/test/java/com/baeldung/file/FileWriterTest.java
@@ -15,7 +15,7 @@ import com.baeldung.util.StreamUtils;
 
 public class FileWriterTest {
     
-    public static final String fileName = "src/main/resources/countries.txt";
+    public static final String fileName = "src/main/resources/countries.properties";
 
     @Test
     public void whenAppendToFileUsingFileWriter_thenCorrect() throws IOException {
diff --git a/core-java/src/test/java/com/baeldung/file/FilesTest.java b/core-java/src/test/java/com/baeldung/file/FilesTest.java
index 7da2d5ce7b..bd39d004d3 100644
--- a/core-java/src/test/java/com/baeldung/file/FilesTest.java
+++ b/core-java/src/test/java/com/baeldung/file/FilesTest.java
@@ -16,7 +16,7 @@ import com.baeldung.util.StreamUtils;
 
 public class FilesTest {
 
-    public static final String fileName = "src/main/resources/countries.txt";
+    public static final String fileName = "src/main/resources/countries.properties";
 
     @Test
     public void whenAppendToFileUsingFiles_thenCorrect() throws IOException {
diff --git a/core-java/src/test/java/com/baeldung/file/GuavaTest.java b/core-java/src/test/java/com/baeldung/file/GuavaTest.java
index b17b12c464..5caa59e596 100644
--- a/core-java/src/test/java/com/baeldung/file/GuavaTest.java
+++ b/core-java/src/test/java/com/baeldung/file/GuavaTest.java
@@ -18,7 +18,7 @@ import com.google.common.io.Files;
 
 public class GuavaTest {
 
-    public static final String fileName = "src/main/resources/countries.txt";
+    public static final String fileName = "src/main/resources/countries.properties";
 
     @Test
     public void whenAppendToFileUsingGuava_thenCorrect() throws IOException {