fix: now properly generating hex escape sequences

Fixes #11

Author: quintesse

src/main/java/org/codejive/properties/Properties.java

@@ -590,7 +590,7 @@ private String escape(String raw, boolean forKey) {
                 replace(
                         raw,
                         "[^\\x{0000}-\\x{00FF}]",
-                        m -> "\\\\u" + Integer.toString(m.group(0).charAt(0), 16));
+                        m -> "\\\\u" + String.format("%04x", (int)m.group(0).charAt(0)));
         return raw;
     }
 

src/test/java/org/codejive/properties/TestProperties.java

@@ -327,6 +327,16 @@ void testPutNull() throws IOException, URISyntaxException {
                 .isInstanceOf(NullPointerException.class);
     }
 
+    @Test
+    void testPutUnicode() throws IOException, URISyntaxException {
+        Properties p = new Properties();
+        p.put("test", "الألبانية");
+        StringWriter sw = new StringWriter();
+        p.store(sw);
+        assertThat(sw.toString())
+                .isEqualTo(readAll(getResource("/test-putunicode.properties")));
+    }
+
     @Test
     void testRemoveFirst() throws IOException, URISyntaxException {
         Properties p = Properties.loadProperties(getResource("/test.properties"));

src/test/resources/test-putunicode.properties

@@ -0,0 +1 @@
+test=\u0627\u0644\u0623\u0644\u0628\u0627\u0646\u064a\u0629