add more tests and support two options

org.eclipse.jdt.core.manipulation/core extension/org/eclipse/jdt/internal/corext/fix/CleanUpConstants.java

@@ -2352,7 +2352,7 @@ public class CleanUpConstants {
 	/**
 	 *
 	 */
-	public static final String EXPLICITENCODING_CLEANUP= "org.eclipse.jdt.ui.cleanup.explicit_encoding"; //$NON-NLS-1$
+	public static final String EXPLICITENCODING_CLEANUP= "cleanup.explicit_encoding"; //$NON-NLS-1$
 
 	/**
 	 * Don't change behavior - just replace or insert to make use of platform encoding visible in the code.

org.eclipse.jdt.core.manipulation/core extension/org/eclipse/jdt/internal/corext/fix/helper/ChangeBehavior.java

@@ -53,7 +53,8 @@ protected String computeCharsetforPreview() {
 	ENFORCE_UTF8() {
 		@Override
 		protected Expression computeCharsetASTNode(final CompilationUnitRewrite cuRewrite, AST ast, String charset) {
-			Expression callToCharsetDefaultCharset= addCharsetUTF8(cuRewrite, ast, charset);
+			String charset2= charset==null?"UTF_8":charset; //$NON-NLS-1$
+			Expression callToCharsetDefaultCharset= addCharsetUTF8(cuRewrite, ast, charset2);
 			return callToCharsetDefaultCharset;
 		}
 

org.eclipse.jdt.ui.tests/ui/org/eclipse/jdt/ui/tests/quickfix/AssistQuickFixTest12.java

@@ -17,7 +17,6 @@
 
 import org.junit.After;
 import org.junit.Before;
-import org.junit.Ignore;
 import org.junit.Rule;
 import org.junit.Test;
 
@@ -123,7 +122,6 @@ enum Day {
 		assertEqualStringsIgnoreOrder(new String[] { preview }, new String[] { expected });
 	}
 
-	@Ignore("https://github.com/eclipse-jdt/eclipse.jdt.ui/issues/1792")
 	@Test
 	public void testSplitSwitchCaseLabelRuleStatement() throws Exception {
 		fJProject1= JavaProjectHelper.createJavaProject("TestProject1", "bin");