As a part of this issue, we have to kill the mutation listed below and remove the suppression from pitest-javadoc-suppression.xml

How to Kill the Mutation

1) Take 1 mutation and apply to the code

Pick up the one mutation from the pitest-javadoc-suppression.xml file or for better understanding you can generate the pitest report as well by Following Steps
and finally hardcode the mutation.

How to hardcode the mutation
For better understanding of mutatnt, That how it works. Please checkout Pitest Doc In this you will find the detail explaination of each mutant with example.

2) Send the pr and generate the report

After hardcoding the code please send a pull request and try to generate the regression Report. If Regression report found the diff then you got your test cases. use that part of code as your input and create a test.

How to generate the Regression Report
To learn how to generate the regression report Please go through the Following link.
https://github.com/checkstyle/contribution/tree/master/checkstyle-tester#report-generation

After reading this you found the 2 method two genrate the report please try to generate the report with Github Action.
For example https://github.com/checkstyle/contribution/tree/master/checkstyle-tester#generation-examples
Basically you have to generate the 2 report in with project file

1. Project-list-1
2. Project-list-2
3. Project-list-3

3) Removal of code

If no diff found from all the report just follow the mutation apply the changes and update the pr.

Apart of this for more detailed explaination please go through Wiki-Page and Pit Documentation

Example of how we did not find by report test case that kill mutation #13342 and we simply updated code as pitest mutated.

Example of how to share analytical explanation on why removal of code is ok - #14410

List of survivals to kill mutation

please always choose single mutation for Pull Request.

  <mutation unstable="false">
    <sourceFile>JavadocTagInfo.java</sourceFile>
    <mutatedClass>com.puppycrawl.tools.checkstyle.checks.javadoc.JavadocTagInfo$15</mutatedClass>
    <mutatedMethod>isValidOn</mutatedMethod>
    <mutator>org.pitest.mutationtest.engine.gregor.mutators.RemoveConditionalMutator_EQUAL_IF</mutator>
    <description>removed conditional - replaced equality check with true</description>
    <lineContent>&amp;&amp; varType.getFirstChild().getType() == TokenTypes.ARRAY_DECLARATOR</lineContent>
  </mutation>

  <mutation unstable="false">
    <sourceFile>JavadocTagInfo.java</sourceFile>
    <mutatedClass>com.puppycrawl.tools.checkstyle.checks.javadoc.JavadocTagInfo$15</mutatedClass>
    <mutatedMethod>isValidOn</mutatedMethod>
    <mutator>org.pitest.mutationtest.engine.gregor.mutators.RemoveConditionalMutator_EQUAL_IF</mutator>
    <description>removed conditional - replaced equality check with true</description>
    <lineContent>return astType == TokenTypes.VARIABLE_DEF</lineContent>
  </mutation>

Abandoned work but might be good to look at:
#13601
#13600

Already done mutation kills:

1) JavadocParagraphCheck

• MemberVariableMutator on DetailNode newLine = JavadocUtil.getPreviousSibling(node)

3) JavadocStyleCheck

• NonVoidMethodCallMutator on builder.deleteCharAt(index)
• NonVoidMethodCallMutator on if (Character.isWhitespace(builder.charAt(index)))
• NonVoidMethodCallMutator on if (Character.isWhitespace(builder.charAt(index)))
• RemoveConditionalMutator_EQUAL_ELSE on if (Character.isWhitespace(builder.charAt(index))) {
• RemoveConditionalMutator_EQUAL_ELSE on if (Character.isWhitespace(builder.charAt(index))) {
• RemoveConditionalMutator_EQUAL_IF on if (Character.isWhitespace(builder.charAt(index)))
• RemoveIncrementsMutator on index += 2;
• NakedReceiverMutator on builder.deleteCharAt(index)

4) JavadocMethodCheck

• NonVoidMethodCallMutator on columnNo = fullIdent.getColumnNo()

• MemberVariableMutator on columnNo = fullIdent.getColumnNo()

• NonVoidMethodCallMutator on .lineNo = fullIdent.getLineNo();

• MemberVariableMutator on lineNo = fullIdent.getLineNo();

• ArgumentPropagationMutator on final int col = calculateTagColumn(noargCurlyMatcher, i, startColumnNumber)

• NonVoidMethodCallMutator on final Token token = new Token(tag.getFirstArg(), tag.getLineNo(), tag

• NonVoidMethodCallMutator on final int col = calculateTagColumn(noargCurlyMatcher, i, startColumnNumber)

• NonVoidMethodCallMutator on foundThrows.add(documentedClassInfo.getName().getText())

• NonVoidMethodCallMutator on foundThrows.add(documentedClassInfo.getName().getText())

• RemoveConditionalMutator_EQUAL_ELSE on if (class1.contains(separator) || class2.contains(separator)) {

• RemoveConditionalMutator_EQUAL_IF on if (arg1.startsWith(ELEMENT_START) && arg1.endsWith(ELEMENT_END))

• RemoveConditionalMutator_EQUAL_IF on if (child.getType() == TokenTypes.PARAMETER_DEF) {

• RemoveConditionalMutator_EQUAL_IF on if (class1.contains(separator) || class2.contains(separator)) {

• RemoveConditionalMutator_EQUAL_IF on if (ancestor.getType() == TokenTypes.LITERAL_TRY

• RemoveConditionalMutator_EQUAL_IF on return surroundingAccessModifier != null

• NakedReceiverMutator on final DetailAST blockAst = methodAst.findFirstToken(TokenTypes.SLIST)

• NakedReceiverMutator on DetailAST ancestor = throwAst.getParent();

2) JavadocMethodCheck$Token

• NonVoidMethodCallMutator on columnNo = fullIdent.getColumnNo();
• NonVoidMethodCallMutator - Issue #13321: Kill mutation for JavadocMethod-7 #13342
• MemberVariableMutator on columnNo = fullIdent.getColumnNo();
• MemberVariableMutator on lineNo = fullIdent.getLineNo();
• MemberVariableMutator on lineNo = fullIdent.getLineNo()

5) JavadocNodeImpl

• NonVoidMethodCallMutator on + ", children=" + Objects.hashCode(children)

6) JavadocTagInfo$15

• RemoveConditionalMutator_EQUAL_IF on varType.getFirstChild().getType() == TokenTypes.ARRAY_DECLARATOR
• RemoveConditionalMutator_EQUAL_IF on return astType == TokenTypes.VARIABLE_DE
  Issue #13501: Kill mutation for JavadocTagInfo4 #13601
  Issue #13501: Kill mutation for JavadocTagInfo3 #13600

7) JavadocTagInfo$14

• RemoveConditionalMutator_EQUAL_IF (1) on return astType == TokenTypes.METHOD_DEF
  Issue #13501: Kill mutation for JavadocTagInfo2 #13599

8) JavadocTagInfo$11

• RemoveConditionalMutator_EQUAL_IF (1) on return astType == TokenTypes.METHOD_DEF
  Issue #13501: Kill mutation for JavadocTagInfo #13598.

9) TagParser

• ArgumentPropagationMutator on Point position = findChar(text, '<', new Point(0, 0))
• ArgumentPropagationMutator on toPoint = findChar(text, '>', getNextPoint(text, toPoint))
• ArgumentPropagationMutator on toPoint = findChar(text, '>', toPoint)
• NonVoidMethodCallMutator on (Character.isJavaIdentifierStart(text.charAt(position))
• NonVoidMethodCallMutator on (Character.isJavaIdentifierStart(text.charAt(position))
• RemoveConditionalMutator_EQUAL_ELSE on if (incompleteTag) {
• RemoveConditionalMutator_EQUAL_ELSE on .substring(0, toPoint.getColumnNo() + 1).endsWith("-->"))
• RemoveConditionalMutator_EQUAL_IF on (Character.isJavaIdentifierStart(text.charAt(position))
• NakedReceiverMutator on text = text.substring(column).trim()
• RemoveConditionalMutator_ORDER_ELSE while (toPoint.getLineNo() < text.length && !text[toPoint.getLineNo()]

10) AbstractJavadocCheck

• NonVoidMethodCallMutator on JavadocUtil.getTokenName(javadocTokenId), getClass().getName())
• NonVoidMethodCallMutator on avadocToken, getClass().getName()
• NonVoidMethodCallMutator on blockCommentNode.getColumnNo())
• NonVoidMethodCallMutator on waitsForProcessing = shouldBeProcessed(curNode);
• RemoveConditionalMutator_EQUAL_ELSE on if (curNode != null) {
• RemoveConditionalMutator_EQUAL_IF on if (getRequiredJavadocTokens().length != 0)
• RemoveConditionalMutator_EQUAL_IF on if (toVisit == null) {
  Issue #13501: Kill mutation for AbstarctJavadoc #13602