Prepare IdeHookTest to run in configuration cache mode.

lib/src/main/java/com/diffplug/spotless/TestingOnly.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2024 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;
+
+import java.util.Locale;
+
+/** These FormatterStep are meant to be used for testing only. */
+public class TestingOnly {
+	public static FormatterStep lowercase() {
+		return FormatterStep.create("lowercase", "lowercaseStateUnused", unused -> TestingOnly::lowercase);
+	}
+
+	private static String lowercase(String raw) {
+		return raw.toLowerCase(Locale.ROOT);
+	}
+
+	public static FormatterStep diverge() {
+		return FormatterStep.create("diverge", "divergeStateUnused", unused -> TestingOnly::diverge);
+	}
+
+	private static String diverge(String raw) {
+		return raw + " ";
+	}
+}

plugin-gradle/src/test/java/com/diffplug/gradle/spotless/IdeHookTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 DiffPlug
+ * Copyright 2016-2024 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -40,11 +40,11 @@ void before() throws IOException {
 				"spotless {",
 				"  format 'misc', {",
 				"    target 'DIRTY.md', 'CLEAN.md'",
-				"    custom 'lowercase', { str -> str.toLowerCase(Locale.ROOT) }",
+				"    addStep com.diffplug.spotless.TestingOnly.lowercase()",
 				"  }",
 				"  format 'diverge', {",
 				"    target 'DIVERGE.md'",
-				"    custom 'diverge', { str -> str + ' ' }",
+				"    addStep com.diffplug.spotless.TestingOnly.diverge()",
 				"  }",
 				"}");
 		dirty = new File(rootFolder(), "DIRTY.md");