chore: add test for mode-switch

Author: simschla

app/src/test/java/com/diffplug/spotless/cli/SpotlessCLIModeTest.java

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2025 DiffPlug
+ *
+ * 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.diffplug.spotless.cli;
+
+import java.io.IOException;
+
+import org.junit.jupiter.api.Test;
+
+import com.diffplug.spotless.cli.steps.GoogleJavaFormat;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class SpotlessCLIModeTest extends CLIIntegrationHarness {
+
+    @Test
+    void applyModeChangesFilesAndExitsWithCode0() throws IOException {
+        setFile("Java.java").toResource("java/googlejavaformat/JavaCodeUnformatted.test");
+
+        SpotlessCLIRunner.Result result = cliRunner()
+                .withTargets("*.java")
+                .withStep(GoogleJavaFormat.class)
+                .run();
+
+        assertFile("Java.java").sameAsResource("java/googlejavaformat/JavaCodeFormatted.test");
+        assertThat(result.exitCode()).isEqualTo(0);
+    }
+
+    @Test
+    void checkModeLeavesFilesUnchangedAndExitsWithCode1() throws IOException {
+        setFile("Java.java").toResource("java/googlejavaformat/JavaCodeUnformatted.test");
+
+        SpotlessCLIRunner.Result result = cliRunner()
+                .withTargets("*.java")
+                .withOption("--mode", "check")
+                .withStep(GoogleJavaFormat.class)
+                .runAndFail();
+
+        assertFile("Java.java").sameAsResource("java/googlejavaformat/JavaCodeUnformatted.test");
+        assertThat(result.exitCode()).isEqualTo(1);
+    }
+}