Fix config file save logic in FileBasedMessageStore

Previously, the `saveConfiguredMessage()` method was calling
`configFile.load()` after updating the config values with addAll(),
which reloaded the file from disk and discarded all in-memory changes.
This resulted in config updates being lost while only the HTML file was
saved.

Fix this by removing the `configFile.load()` call ensuring that
configuration changes are properly persisted to the config file along
with the HTML content.

Change-Id: I60dd739e6e74802437164ef218ef98eb0afdf0f7

BUILD

diff --git a/BUILD b/BUILD
index b517141..95ed97f 100644
--- a/BUILD
+++ b/BUILD
@@ -1,5 +1,12 @@
-load("//tools/bzl:plugin.bzl", "gerrit_plugin")
+load("@rules_java//java:defs.bzl", "java_library")
 load("//tools/bzl:js.bzl", "gerrit_js_bundle")
+load("//tools/bzl:junit.bzl", "junit_tests")
+load(
+    "//tools/bzl:plugin.bzl",
+    "PLUGIN_DEPS",
+    "PLUGIN_TEST_DEPS",
+    "gerrit_plugin",
+)
 
 gerrit_plugin(
     name = "messageoftheday",
@@ -20,3 +27,17 @@
     srcs = glob(["gr-messageoftheday/*.js"]),
     entry_point = "gr-messageoftheday/plugin.js",
 )
+
+junit_tests(
+    name = "messageoftheday_tests",
+    srcs = glob(["src/test/java/**/*.java"]),
+    tags = ["messageoftheday"],
+    deps = [":messageoftheday__plugin_test_deps"],
+)
+
+java_library(
+    name = "messageoftheday__plugin_test_deps",
+    testonly = 1,
+    visibility = ["//visibility:public"],
+    exports = PLUGIN_DEPS + PLUGIN_TEST_DEPS + [":messageoftheday__plugin"],
+)

src/main/java/com/googlesource/gerrit/plugins/messageoftheday/FileBasedMessageStore.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/FileBasedMessageStore.java b/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/FileBasedMessageStore.java
index 4c40d85..4a3e8dc 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/FileBasedMessageStore.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/FileBasedMessageStore.java
@@ -82,7 +82,7 @@
 
   @Override
   public void saveConfiguredMessage(ConfiguredMessage message) throws MessageStoreException {
-    FileBasedConfig configFile = new FileBasedConfig(message.config(), cfgFile, FS.DETECTED);
+    FileBasedConfig configFile = new FileBasedConfig(cfgFile, FS.DETECTED);
 
     addAll(configFile, message.config());
 
@@ -96,9 +96,8 @@
     }
 
     try {
-      configFile.load();
       configFile.save();
-    } catch (IOException | ConfigInvalidException e) {
+    } catch (IOException e) {
       throw new MessageStoreException("Failed to save config", e);
     }
   }

src/test/java/com/googlesource/gerrit/plugins/messageoftheday/FileBasedMessageStoreTest.java

diff --git a/src/test/java/com/googlesource/gerrit/plugins/messageoftheday/FileBasedMessageStoreTest.java b/src/test/java/com/googlesource/gerrit/plugins/messageoftheday/FileBasedMessageStoreTest.java
new file mode 100644
index 0000000..13c53f9
--- /dev/null
+++ b/src/test/java/com/googlesource/gerrit/plugins/messageoftheday/FileBasedMessageStoreTest.java
@@ -0,0 +1,75 @@
+// Copyright (C) 2026 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.googlesource.gerrit.plugins.messageoftheday;
+
+import static com.google.common.truth.Truth.assertThat;
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import java.io.File;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.storage.file.FileBasedConfig;
+import org.eclipse.jgit.util.FS;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+public class FileBasedMessageStoreTest {
+  private static final String SECTION_MESSAGE = "message";
+  private static final String MESSAGE_ID = "test-message";
+  private static final String HTML_CONTENT = "<p>Hello World</p>";
+  private static final String EXPIRES_AT = "20260323:1400";
+
+  @Rule public TemporaryFolder tempFolder = new TemporaryFolder();
+
+  private File cfgFile;
+  private Path dataDir;
+  private FileBasedMessageStore store;
+
+  @Before
+  public void setUp() throws Exception {
+    cfgFile = tempFolder.newFile("messageoftheday.config");
+    dataDir = tempFolder.newFolder("data").toPath();
+    store = new FileBasedMessageStore(cfgFile, dataDir);
+  }
+
+  @Test
+  public void writesHtmlFileWithCorrectContent() throws Exception {
+    Config config = new Config();
+    config.setString(SECTION_MESSAGE, null, "id", MESSAGE_ID);
+
+    store.saveConfiguredMessage(new ConfiguredMessage(config, HTML_CONTENT));
+
+    Path htmlFile = dataDir.resolve(MESSAGE_ID + ".html");
+    assertThat(Files.exists(htmlFile)).isTrue();
+    assertThat(Files.readString(htmlFile, UTF_8)).isEqualTo(HTML_CONTENT);
+  }
+
+  @Test
+  public void writesConfigFileWithCorrectValues() throws Exception {
+    Config config = new Config();
+    config.setString(SECTION_MESSAGE, null, "id", MESSAGE_ID);
+    config.setString(SECTION_MESSAGE, null, "expiresAt", EXPIRES_AT);
+
+    store.saveConfiguredMessage(new ConfiguredMessage(config, HTML_CONTENT));
+
+    FileBasedConfig savedConfig = new FileBasedConfig(cfgFile, FS.DETECTED);
+    savedConfig.load();
+    assertThat(savedConfig.getString(SECTION_MESSAGE, null, "id")).isEqualTo(MESSAGE_ID);
+    assertThat(savedConfig.getString(SECTION_MESSAGE, null, "expiresAt")).isEqualTo(EXPIRES_AT);
+  }
+}