test: trailing comma management strategy only add

Author: greyhairredbear

testlib/src/main/resources/kotlin/ktfmt/trailing-commas-only-add.clean

@@ -0,0 +1,13 @@
+import a.*
+
+fun foo(
+    paramA: String,
+    paramB: Int,
+    anotherParamIsHere: Float,
+    myLongParamNameIsHere: CustomType,
+    lastParam: Boolean,
+) = Unit
+
+fun bar(
+    myLongParamNameIsHereButDoesNotWrap: Int,
+) = Unit

testlib/src/main/resources/kotlin/ktfmt/trailing-commas-only-add.dirty

@@ -0,0 +1,8 @@
+import a.*
+
+fun foo(paramA: String,paramB : Int , anotherParamIsHere: Float ,myLongParamNameIsHere: CustomType
+,lastParam: Boolean ) = Unit
+
+fun bar(
+    myLongParamNameIsHereButDoesNotWrap: Int,
+) = Unit

testlib/src/test/java/com/diffplug/spotless/kotlin/KtfmtStepTest.java

@@ -70,7 +70,16 @@ void behaviorWithTrailingCommas() throws Exception {
 		StepHarness.forStep(step).testResource("kotlin/ktfmt/trailing-commas.dirty", "kotlin/ktfmt/trailing-commas.clean");
 	}
 
-	// TODO: test trailing comma only add
+	@Test
+	void behaviorWithTrailingCommaManagementStrategyOnlyAdd() {
+		KtfmtStep.KtfmtFormattingOptions options = new KtfmtStep.KtfmtFormattingOptions();
+		options.setTrailingCommaManagementStrategy(KtfmtStep.TrailingCommaManagementStrategy.ONLY_ADD);
+		FormatterStep step = KtfmtStep.create("0.58", TestProvisioner.mavenCentral(), KtfmtStep.Style.KOTLINLANG, options);
+		StepHarness.forStep(step).testResource(
+			"kotlin/ktfmt/trailing-commas-only-add.dirty",
+			"kotlin/ktfmt/trailing-commas-only-add.clean"
+		);
+	}
 
 	// TODO: test before 0.57