added FunctionNameTooShort test in bestpractices category for Kotlin, with unit test cases

pmd-kotlin/src/main/resources/category/kotlin/bestpractices.xml

@@ -0,0 +1,39 @@
+<?xml version="1.0"?>
+
+<ruleset name="Best Practices"
+    xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 https://pmd.sourceforge.io/ruleset_2_0_0.xsd">
+
+    <description>
+Rules which enforce generally accepted best practices.
+    </description>
+
+    <rule name="FunctionNameTooShort"
+          since="7.0"
+          language="kotlin"
+          message="Function names should have non-cryptic and clear names."
+          class="net.sourceforge.pmd.lang.rule.XPathRule"
+          typeResolution="true"
+          externalInfoUrl="https://pmd.github.io/pmd/pmd_rules_kotlin_bestpractices.html#functionametooshort">
+        <description>
+            Function names should be easy to understand and describe the intention. Makes developers happy.
+        </description>
+        <priority>3</priority>
+        <properties>
+            <property name="version" value="3.1"/>
+            <property name="xpath">
+                <value><![CDATA[
+                    //FunctionDeclaration/SimpleIdentifier/T-Identifier[string-length(@Text) < 3]
+                ]]></value>
+            </property>
+        </properties>
+        <example>
+            <![CDATA[
+fun cl() {} // violation, no unavailable attribute added to the function declaration
+
+fun calculateLayout() // no violation
+]]>
+        </example>
+    </rule>
+</ruleset>

pmd-kotlin/src/main/resources/category/kotlin/categories.properties

@@ -2,18 +2,16 @@
 # BSD-style license; for more info see http://pmd.sourceforge.net/license.html
 #
 
-rulesets.filenames=
-
+rulesets.filenames=\
+    category/kotlin/bestpractices.xml
 #
 # categories without rules
 #
 
-# category/kotlin/bestpractices.xml,\
-#    category/kotlin/errorprone.xml
-
 # category/kotlin/codestyle.xml
 # category/kotlin/design.xml
 # category/kotlin/documentation.xml
+# category/kotlin/errorprone.xml
 # category/kotlin/multithreading.xml
 # category/kotlin/performance.xml
 # category/kotlin/security.xml

pmd-kotlin/src/main/resources/rulesets/kotlin/rulesets.properties

@@ -0,0 +1,7 @@
+#
+# BSD-style license; for more info see http://pmd.sourceforge.net/license.html
+#
+
+rulesets.filenames=\
+    category/kotlin/bestpractices.xml
+

pmd-kotlin/src/test/java/net/sourceforge/pmd/lang/kotlin/rule/bestpractices/FunctionNameTooShortTest.java

@@ -0,0 +1,11 @@
+/**
+ * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
+ */
+
+package net.sourceforge.pmd.lang.kotlin.rule.bestpractices;
+
+import net.sourceforge.pmd.testframework.PmdRuleTst;
+
+public class FunctionNameTooShortTest extends PmdRuleTst {
+    // no additional unit tests
+}

pmd-kotlin/src/test/resources/net/sourceforge/pmd/lang/kotlin/rule/bestpractices/xml/FunctionNameTooShort.xml

@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<test-data
+    xmlns="http://pmd.sourceforge.net/rule-tests"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://pmd.sourceforge.net/rule-tests http://pmd.sourceforge.net/rule-tests_1_0_0.xsd">
+
+    <test-code>
+        <description>Good example #1</description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[
+class GoodBar {
+    fun checkLayout() // good
+}
+     ]]></code>
+    </test-code>
+    <test-code>
+        <description>Bad example #1</description>
+        <expected-problems>2</expected-problems>
+        <expected-linenumbers>2,3</expected-linenumbers>
+        <code><![CDATA[
+class BadBar {
+    fun cl() // bad
+    fun c() // bad
+    fun clr() // good
+}
+     ]]></code>
+    </test-code>
+</test-data>