test(core): add test for ConfigHolder

core/src/test/java/net/okocraft/servermonitor/core/config/ConfigHolderTest.java

@@ -0,0 +1,63 @@
+package net.okocraft.servermonitor.core.config;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardOpenOption;
+import java.util.function.UnaryOperator;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertLinesMatch;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class ConfigHolderTest {
+
+    @Test
+    void testLoading(@TempDir Path dir) throws IOException {
+        var filepath = dir.resolve("config.yml");
+        var defaultConfig = new Config(100, "test");
+        var holder = new ConfigHolder<>(defaultConfig, UnaryOperator.identity());
+
+        { // first loading (saving default config entries)
+            holder.load(filepath);
+
+            assertTrue(Files.isRegularFile(filepath));
+            assertLinesMatch(defaultConfig.asYaml().lines(), Files.readString(filepath, StandardCharsets.UTF_8).lines());
+
+            assertEquals(defaultConfig, holder.get());
+        }
+
+        { // second loading (file changed)
+            var modified = new Config(150, "TEST");
+            modifyAndLoadConfig(filepath, modified, holder, false);
+        }
+
+        { // reloading (file changed)
+            var modified = new Config(500, "TEst");
+            modifyAndLoadConfig(filepath, modified, holder, true);
+        }
+    }
+
+    private static void modifyAndLoadConfig(Path filepath, Config modified, ConfigHolder<Config> holder, boolean reload) throws IOException {
+        Files.writeString(filepath, modified.asYaml(), StandardCharsets.UTF_8, StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING);
+
+        if (reload) {
+            holder.reload(filepath);
+        } else {
+            holder.load(filepath);
+        }
+
+        assertEquals(modified, holder.get());
+    }
+
+    private record Config(int value, String string) {
+        public String asYaml() {
+            return "value: " + this.value + System.lineSeparator() +
+                   "string: " + this.string + System.lineSeparator();
+        }
+    }
+}