Add a test for the license header reatchet behavior in the maven plugin.

plugin-maven/src/test/java/com/diffplug/spotless/maven/generic/LicenseHeaderRatchetTest.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2020 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.maven.generic;
+
+import java.io.IOException;
+import java.time.YearMonth;
+
+import org.eclipse.jgit.api.Git;
+import org.junit.Test;
+
+import com.diffplug.spotless.maven.MavenIntegrationHarness;
+
+public class LicenseHeaderRatchetTest extends MavenIntegrationHarness {
+	private static final String NOW = String.valueOf(YearMonth.now().getYear());
+
+	private static final String TEST_JAVA = "src/main/java/pkg/Test.java";
+	private static final String CONTENT = "package pkg;\npublic class Test {}";
+
+	private void setRatchetFrom(String ratchetFrom) throws IOException {
+		writePomWithJavaSteps(
+				"<licenseHeader>",
+				"  <content>/** $YEAR */</content>",
+				"</licenseHeader>",
+				ratchetFrom);
+	}
+
+	private void assertUnchanged(String year) throws Exception {
+		assertTransform(year, year);
+	}
+
+	private void assertTransform(String yearBefore, String yearAfter) throws Exception {
+		setFile(TEST_JAVA).toContent("/** " + yearBefore + " */\n" + CONTENT);
+		mavenRunner().withArguments("spotless:apply").runNoError();
+		assertFile(TEST_JAVA).hasContent("/** " + yearAfter + " */\n" + CONTENT);
+	}
+
+	private void testSuiteUpdateWithLatest(boolean update) throws Exception {
+		if (update) {
+			assertTransform("2003", "2003-" + NOW);
+			assertTransform("2003-2005", "2003-" + NOW);
+		} else {
+			assertUnchanged("2003");
+			assertUnchanged("2003-2005");
+		}
+		assertUnchanged(NOW);
+		assertTransform("", NOW);
+	}
+
+	@Test
+	public void normal() throws Exception {
+		setRatchetFrom("");
+		testSuiteUpdateWithLatest(false);
+	}
+
+	@Test
+	public void ratchetFrom() throws Exception {
+		try (Git git = Git.init().setDirectory(rootFolder()).call()) {
+			git.commit().setMessage("First commit").call();
+		}
+		setRatchetFrom("<ratchetFrom>HEAD</ratchetFrom>");
+		testSuiteUpdateWithLatest(true);
+	}
+}