Because there are a few legitimate reasons to not roundtrip.

Author: nedtwigg

testlib/src/main/java/com/diffplug/spotless/StepHarness.java

@@ -52,6 +52,16 @@ public static StepHarness forFormatter(Formatter formatter) {
 		return new StepHarness(formatter, RoundTrip.ASSERT_EQUAL);
 	}
 
+	public static StepHarness forStepNoRoundtrip(FormatterStep step) {
+		return new StepHarness(Formatter.builder()
+				.steps(Arrays.asList(step))
+				.lineEndingsPolicy(LineEnding.UNIX.createPolicy())
+				.encoding(StandardCharsets.UTF_8)
+				.rootDir(Paths.get(""))
+				.exceptionPolicy(new FormatExceptionPolicyStrict())
+				.build(), RoundTrip.DONT_ROUNDTRIP);
+	}
+
 	/** Asserts that the given element is transformed as expected, and that the result is idempotent. */
 	public StepHarness test(String before, String after) {
 		String actual = formatter().compute(LineEnding.toUnix(before), new File(""));

testlib/src/test/java/com/diffplug/spotless/generic/FenceStepTest.java

@@ -29,14 +29,13 @@
 import com.diffplug.spotless.FormatterStep;
 import com.diffplug.spotless.ResourceHarness;
 import com.diffplug.spotless.StepHarness;
-import com.diffplug.spotless.StepHarnessWithFile;
 
 class FenceStepTest extends ResourceHarness {
 	@Test
 	void single() {
 		FormatterStep fence = FenceStep.named("fence").openClose("spotless:off", "spotless:on")
 				.preserveWithin(Arrays.asList(createNeverUpToDateSerializable("lowercase", String::toLowerCase)));
-		StepHarness harness = StepHarness.forSteps(fence);
+		StepHarness harness = StepHarness.forStepNoRoundtrip(fence);
 		harness.test(
 				StringPrinter.buildStringFromLines(
 						"A B C",
@@ -56,7 +55,7 @@ void single() {
 	void multiple() {
 		FormatterStep fence = FenceStep.named("fence").openClose("spotless:off", "spotless:on")
 				.preserveWithin(Arrays.asList(createNeverUpToDateSerializable("lowercase", String::toLowerCase)));
-		StepHarness harness = StepHarness.forSteps(fence);
+		StepHarness harness = StepHarness.forStepNoRoundtrip(fence);
 		harness.test(
 				StringPrinter.buildStringFromLines(
 						"A B C",
@@ -90,9 +89,8 @@ void multiple() {
 	void broken() {
 		FormatterStep fence = FenceStep.named("fence").openClose("spotless:off", "spotless:on")
 				.preserveWithin(Arrays.asList(createNeverUpToDateSerializable("uppercase", String::toUpperCase)));
-		StepHarnessWithFile harness = StepHarnessWithFile.forStep(this, fence);
 		// this fails because uppercase turns spotless:off into SPOTLESS:OFF, etc
-		harness.testExceptionMsg(newFile("test"), StringPrinter.buildStringFromLines("A B C",
+		StepHarness.forStepNoRoundtrip(fence).testExceptionMsg(StringPrinter.buildStringFromLines("A B C",
 				"spotless:off",
 				"D E F",
 				"spotless:on",
@@ -103,7 +101,7 @@ void broken() {
 	void andApply() {
 		FormatterStep fence = FenceStep.named("fence").openClose("<lower>", "</lower>")
 				.applyWithin(Arrays.asList(createNeverUpToDateSerializable("lowercase", String::toLowerCase)));
-		StepHarness.forSteps(fence).test(
+		StepHarness.forStepNoRoundtrip(fence).test(
 				StringPrinter.buildStringFromLines(
 						"A B C",
 						"<lower>",
@@ -152,5 +150,6 @@ public String getName() {
 		public String format(String rawUnix, File file) throws Exception {
 			return formatterFunc.apply(rawUnix, file);
 		}
+
 	}
 }

testlib/src/test/java/com/diffplug/spotless/java/GoogleJavaFormatStepTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2023 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.
@@ -64,7 +64,7 @@ void behavior() throws Exception {
 	@Test
 	void versionBelowMinimumRequiredVersionIsNotAllowed() throws Exception {
 		FormatterStep step = GoogleJavaFormatStep.create("1.2", "AOSP", TestProvisioner.mavenCentral());
-		StepHarness.forStep(step)
+		StepHarness.forStepNoRoundtrip(step)
 				.testResourceExceptionMsg("java/googlejavaformat/JavaCodeWithLicenseUnformatted.test")
 				.contains("you are using 1.2");
 	}
@@ -73,7 +73,7 @@ void versionBelowMinimumRequiredVersionIsNotAllowed() throws Exception {
 	@EnabledForJreRange(min = JAVA_16)
 	void versionBelowOneDotTenIsNotAllowed() throws Exception {
 		FormatterStep step = GoogleJavaFormatStep.create("1.9", "AOSP", TestProvisioner.mavenCentral());
-		StepHarness.forStep(step)
+		StepHarness.forStepNoRoundtrip(step)
 				.testResourceExceptionMsg("java/googlejavaformat/JavaCodeWithLicenseUnformatted.test")
 				.contains("you are using 1.9");
 	}