diff --git a/Core/src/test/java/com/songoda/core/configuration/ReadOnlyConfigEntryTest.java b/Core/src/test/java/com/songoda/core/configuration/ReadOnlyConfigEntryTest.java
index 059e43c3..a01bd2c4 100644
--- a/Core/src/test/java/com/songoda/core/configuration/ReadOnlyConfigEntryTest.java
+++ b/Core/src/test/java/com/songoda/core/configuration/ReadOnlyConfigEntryTest.java
@@ -28,4 +28,22 @@ public class ReadOnlyConfigEntryTest {
         assertNull(entry.getDefaultValue());
         assertNull(entry.getUpgradeSteps());
     }
+
+    @Test
+    void testWritingMethodsDoingNothing() {
+        YamlConfiguration config = new YamlConfiguration();
+        ConfigEntry entry = new ReadOnlyConfigEntry(config, "key");
+
+        assertThrows(UnsupportedOperationException.class, () -> entry.setDefaultValue("value"));
+        assertThrows(UnsupportedOperationException.class, () -> entry.withDefaultValue("value"));
+        assertThrows(UnsupportedOperationException.class, () -> entry.withComment("A comment."));
+        assertThrows(UnsupportedOperationException.class, () -> entry.withUpgradeStep(0, "old-key"));
+        assertThrows(UnsupportedOperationException.class, () -> entry.set("value"));
+
+        assertNull(entry.getDefaultValue());
+        assertNull(entry.getUpgradeSteps());
+        assertNull(config.getNodeComment("key"));
+        assertNull(entry.getUpgradeSteps());
+        assertNull(entry.get());
+    }
 }
diff --git a/Core/src/test/java/com/songoda/core/configuration/songoda/SongodaYamlConfigRoundtripTest.java b/Core/src/test/java/com/songoda/core/configuration/songoda/SongodaYamlConfigRoundtripTest.java
index 1e2f6f10..bd2e980b 100644
--- a/Core/src/test/java/com/songoda/core/configuration/songoda/SongodaYamlConfigRoundtripTest.java
+++ b/Core/src/test/java/com/songoda/core/configuration/songoda/SongodaYamlConfigRoundtripTest.java
@@ -5,7 +5,6 @@ import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
-import java.io.File;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -46,7 +45,8 @@ class SongodaYamlConfigRoundtripTest {
         SongodaYamlConfig cfg = new SongodaYamlConfig(testFilePath.toFile())
                 .withVersion(3);
 
-        ConfigEntry cmdFooSuccess = cfg.createEntry("command.foo.success", "Default success value")
+        ConfigEntry cmdFooSuccess = cfg.createEntry("command.foo.success")
+                .withDefaultValue("Default success value")
                 .withComment("This message is shown when the 'foo' command succeeds.")
                 .withUpgradeStep(1, "messages.fooSuccess");
         ConfigEntry range = cfg.createEntry("range")
@@ -69,7 +69,8 @@ class SongodaYamlConfigRoundtripTest {
                     return (int) o + 1;
                 })
                 .withUpgradeStep(3, null, (o) -> "text");
-        ConfigEntry entryWithoutUpgradeStep = cfg.createEntry("entryWithoutUpgradeStep", "Default value")
+        ConfigEntry entryWithoutUpgradeStep = cfg.createEntry("entryWithoutUpgradeStep")
+                .withDefaultValue("Default value")
                 .withComment("This is the entry without an upgrade step");
 
         assertTrue(cfg.init());
diff --git a/Core/src/test/java/com/songoda/core/configuration/songoda/SongodaYamlConfigTest.java b/Core/src/test/java/com/songoda/core/configuration/songoda/SongodaYamlConfigTest.java
index 08537edc..ed5f3c75 100644
--- a/Core/src/test/java/com/songoda/core/configuration/songoda/SongodaYamlConfigTest.java
+++ b/Core/src/test/java/com/songoda/core/configuration/songoda/SongodaYamlConfigTest.java
@@ -4,6 +4,7 @@ import com.songoda.core.configuration.ConfigEntry;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
 
 import java.io.File;
 import java.io.IOException;
@@ -13,6 +14,8 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.Comparator;
 import java.util.Objects;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 import java.util.stream.Stream;
 
 import static org.junit.jupiter.api.Assertions.*;
@@ -34,7 +37,8 @@ class SongodaYamlConfigTest {
         try (Stream<Path> stream = Files.walk(this.tmpDir)) {
             stream
                     .sorted(Comparator.reverseOrder())
-                    .map(Path::toFile).forEach(File::delete);
+                    .map(Path::toFile)
+                    .forEach(File::delete);
         }
     }
 
@@ -94,6 +98,17 @@ class SongodaYamlConfigTest {
         );
     }
 
+    @Test
+    void testWithZeroVersion() throws IOException {
+        SongodaYamlConfig cfg = new SongodaYamlConfig(this.cfg.toFile());
+        cfg.withVersion("version-key", 0, null);
+
+        assertEquals(0, cfg.get("version-key"));
+
+        cfg.save();
+        assertEquals("version-key: 0\n", new String(Files.readAllBytes(this.cfg)));
+    }
+
     @Test
     void testWithNegativeVersion() {
         SongodaYamlConfig cfg = new SongodaYamlConfig(this.cfg.toFile());
@@ -213,4 +228,19 @@ class SongodaYamlConfigTest {
         entry.set("new-value");
         assertEquals("new-value", readOnlyConfigEntry.get());
     }
+
+    @Test
+    void testInit_Failure() {
+        assertTrue(this.cfg.toFile().setWritable(false));
+
+        Logger mockLogger = Mockito.mock(Logger.class);
+        SongodaYamlConfig cfg = new SongodaYamlConfig(this.cfg.toFile(), mockLogger);
+
+        cfg.createEntry("key", "default-value");
+
+        assertFalse(cfg.init());
+        Mockito.verify(mockLogger).log(Mockito.eq(Level.SEVERE), Mockito.anyString(), Mockito.any(IOException.class));
+
+        assertTrue(this.cfg.toFile().setWritable(true));
+    }
 }
diff --git a/Core/src/test/java/com/songoda/core/configuration/yaml/YamlConfigEntryTest.java b/Core/src/test/java/com/songoda/core/configuration/yaml/YamlConfigEntryTest.java
index f9e9dc81..f0cc5ead 100644
--- a/Core/src/test/java/com/songoda/core/configuration/yaml/YamlConfigEntryTest.java
+++ b/Core/src/test/java/com/songoda/core/configuration/yaml/YamlConfigEntryTest.java
@@ -3,6 +3,7 @@ package com.songoda.core.configuration.yaml;
 import com.songoda.core.compatibility.CompatibleMaterial;
 import com.songoda.core.configuration.ConfigEntry;
 import com.songoda.core.configuration.songoda.SongodaYamlConfig;
+import com.songoda.ultimatestacker.core.configuration.Config;
 import org.bukkit.Material;
 import org.junit.jupiter.api.Test;
 
@@ -20,6 +21,18 @@ import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 class YamlConfigEntryTest {
+    @Test
+    void testHas() {
+        YamlConfiguration config = new YamlConfiguration();
+        config.set("key-2", "value-2");
+
+        ConfigEntry entry1 = new YamlConfigEntry(config, "key-1", null);
+        ConfigEntry entry2 = new YamlConfigEntry(config, "key-2", null);
+
+        assertFalse(entry1.has());
+        assertTrue(entry2.has());
+    }
+
     @Test
     void testGetKey() {
         ConfigEntry entry = new YamlConfigEntry(new YamlConfiguration(), "key-1", null);
@@ -42,6 +55,9 @@ class YamlConfigEntryTest {
 
         entry.setDefaultValue("new-value");
         assertEquals("new-value", entry.getDefaultValue());
+
+        entry.withDefaultValue("new-value-2");
+        assertEquals("new-value-2", entry.getDefaultValue());
     }
 
     @Test
@@ -235,5 +251,8 @@ class YamlConfigEntryTest {
         other = new YamlConfigEntry(cfg, "key2", "value2");
         assertNotEquals(entry, other);
         assertNotEquals(entry.hashCode(), other.hashCode());
+
+        assertNotEquals(entry, null);
+        assertNotEquals(entry, "key");
     }
 }