diff --git a/plugins/devkit/devkit-core/intellij.devkit.iml b/plugins/devkit/devkit-core/intellij.devkit.iml
index 2de433272b5d..a2961da857dd 100644
--- a/plugins/devkit/devkit-core/intellij.devkit.iml
+++ b/plugins/devkit/devkit-core/intellij.devkit.iml
@@ -6,6 +6,7 @@
       <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" packagePrefix="org.jetbrains.idea.devkit" />
       <sourceFolder url="file://$MODULE_DIR$/gen" isTestSource="false" generated="true" />
       <sourceFolder url="file://$MODULE_DIR$/resources" type="java-resource" />
+      <sourceFolder url="file://$MODULE_DIR$/testSrc" isTestSource="true" />
     </content>
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />
@@ -63,5 +64,6 @@
     <orderEntry type="module" module-name="intellij.platform.ide.util.netty" />
     <orderEntry type="library" name="CGLIB" level="project" />
     <orderEntry type="module" module-name="intellij.platform.bootstrap" />
+    <orderEntry type="library" scope="TEST" name="JUnit4" level="project" />
   </component>
 </module>
\ No newline at end of file
diff --git a/plugins/devkit/devkit-core/src/commit/KotlinPluginCommitMessageHandlerFactory.kt b/plugins/devkit/devkit-core/src/commit/KotlinPluginCommitMessageHandlerFactory.kt
index 20ba6012b89b..7d9a2ede1e8a 100644
--- a/plugins/devkit/devkit-core/src/commit/KotlinPluginCommitMessageHandlerFactory.kt
+++ b/plugins/devkit/devkit-core/src/commit/KotlinPluginCommitMessageHandlerFactory.kt
@@ -13,26 +13,36 @@ import com.intellij.util.PairConsumer
 import com.intellij.util.io.systemIndependentPath
 import org.jetbrains.idea.devkit.DevKitBundle
 import org.jetbrains.idea.devkit.util.PsiUtil
+import java.io.File
 import kotlin.io.path.extension
-import kotlin.io.path.isRegularFile
 
 class KotlinPluginCommitMessageHandlerFactory : CheckinHandlerFactory() {
 
-  companion object {
-    private const val kotlinPluginPath = "plugins/kotlin/"
-    private val pathsToIgnore = setOf("/test/", "/testData/")
-    private val fileExtensionsNotToTrack = setOf("iml", "md")
-    private val commitMessageRegex = Regex(".*KTIJ-\\d+.*", RegexOption.DOT_MATCHES_ALL /* line breaks matter */)
-  }
-
   override fun createHandler(panel: CheckinProjectPanel, commitContext: CommitContext): CheckinHandler =
     YouTrackIssueCommitMessageHandler(panel)
 
 
-  private class YouTrackIssueCommitMessageHandler(private val checkinPanel: CheckinProjectPanel) : CheckinHandler() {
+  internal class YouTrackIssueCommitMessageHandler(private val checkinPanel: CheckinProjectPanel) : CheckinHandler() {
 
     companion object {
-      const val HANDLER_ENABLED_KEY = "kotlin.commit.message.validation.enabled"
+      private const val HANDLER_ENABLED_KEY = "kotlin.commit.message.validation.enabled"
+      private const val KOTLIN_PLUGIN_PATH = "plugins/kotlin/"
+      private val pathsToIgnore = setOf("/test/", "/testData/", "/fleet/plugins/kotlin/")
+      private val fileExtensionsNotToTrack = setOf("iml", "md")
+      private val commitMessageRegex = Regex(".*KTIJ-\\d+.*", RegexOption.DOT_MATCHES_ALL /* line breaks matter */)
+
+      internal fun selectedFilesBelongToKotlinIdePlugin(files: Collection<File>): Boolean {
+        return files.asSequence()
+          .map { file -> file.toPath() }
+          .any { path ->
+            val siPath = path.systemIndependentPath
+            path.extension !in fileExtensionsNotToTrack
+            && siPath.contains(KOTLIN_PLUGIN_PATH)
+            && pathsToIgnore.none { siPath.contains(it) }
+          }
+      }
+
+      internal fun commitMessageIsCorrect(message: String): Boolean = message.matches(commitMessageRegex)
     }
 
     private val project = checkinPanel.project
@@ -52,7 +62,7 @@ class KotlinPluginCommitMessageHandlerFactory : CheckinHandlerFactory() {
 
       if (!messageHandlerEnabled
         || !commitMessageShouldBeChecked()
-        || checkinPanel.commitMessage.matches(commitMessageRegex)
+        || commitMessageIsCorrect(checkinPanel.commitMessage)
       ) {
         return ReturnResult.COMMIT // as is
       }
@@ -73,18 +83,6 @@ class KotlinPluginCommitMessageHandlerFactory : CheckinHandlerFactory() {
     }
 
     private fun commitMessageShouldBeChecked(): Boolean =
-      PsiUtil.isIdeaProject(project) && selectedFilesBelongToKotlinIdePlugin()
-
-    private fun selectedFilesBelongToKotlinIdePlugin(): Boolean {
-      return checkinPanel.files.asSequence()
-        .map { file -> file.toPath() }
-        .any { path ->
-          val siPath = path.systemIndependentPath
-          path.isRegularFile()
-            && path.extension !in fileExtensionsNotToTrack
-            && siPath.contains(kotlinPluginPath)
-            && pathsToIgnore.none { siPath.contains(it) }
-        }
-    }
+      PsiUtil.isIdeaProject(project) && selectedFilesBelongToKotlinIdePlugin(checkinPanel.files)
   }
 }
\ No newline at end of file
diff --git a/plugins/devkit/devkit-core/testSrc/org/jetbrains/idea/devkit/commit/KotlinYouTrackIssueCommitMessageHandlerTest.kt b/plugins/devkit/devkit-core/testSrc/org/jetbrains/idea/devkit/commit/KotlinYouTrackIssueCommitMessageHandlerTest.kt
new file mode 100644
index 000000000000..aa214e49eb24
--- /dev/null
+++ b/plugins/devkit/devkit-core/testSrc/org/jetbrains/idea/devkit/commit/KotlinYouTrackIssueCommitMessageHandlerTest.kt
@@ -0,0 +1,276 @@
+// Copyright 2000-2021 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
+package org.jetbrains.idea.devkit.commit
+
+import org.jetbrains.idea.devkit.commit.KotlinPluginCommitMessageHandlerFactory.YouTrackIssueCommitMessageHandler
+import org.junit.Test
+import org.junit.experimental.runners.Enclosed
+import org.junit.runner.RunWith
+import org.junit.runners.Parameterized
+import org.junit.runners.Parameterized.Parameter
+import java.io.File
+import java.nio.file.Paths
+
+@RunWith(Enclosed::class)
+class KotlinYouTrackIssueCommitMessageHandlerTest {
+
+  @RunWith(Parameterized::class)
+  class FilesBelongToPlugin {
+    companion object {
+      @JvmStatic
+      @Parameterized.Parameters(name = "{0}")
+      fun provideTestParameters(): Iterable<List<Pair<String, String>>> {
+        return listOf(
+          listOf(ULTIMATE_KOTLIN_PLUGIN to "File.kt"),
+          listOf(COMMUNITY_KOTLIN_PLUGIN to "File.kt"),
+
+          listOf(ULTIMATE_KOTLIN_PLUGIN to "File.kts"),
+          listOf(COMMUNITY_KOTLIN_PLUGIN to "File.kts"),
+
+          listOf(ULTIMATE_KOTLIN_PLUGIN to "File.java"),
+          listOf(COMMUNITY_KOTLIN_PLUGIN to "File.java"),
+
+          listOf(ULTIMATE_KOTLIN_PLUGIN to "File.properties"),
+          listOf(COMMUNITY_KOTLIN_PLUGIN to "File.properties"),
+
+          listOf(ULTIMATE_KOTLIN_PLUGIN to "File.html"),
+          listOf(COMMUNITY_KOTLIN_PLUGIN to "File.html"),
+
+          listOf(ULTIMATE_KOTLIN_PLUGIN to "File.xml"),
+          listOf(COMMUNITY_KOTLIN_PLUGIN to "File.xml"),
+
+          listOf(
+            COMMUNITY_KOTLIN_PLUGIN to "File.kt",
+            "not-important-dir-A" to "whatever-file",
+            "not-important-dir-B" to "whatever-file"
+          ),
+
+          listOf(
+            "not-important-dir-A" to "whatever-file",
+            COMMUNITY_KOTLIN_PLUGIN to "File.kt",
+            "not-important-dir-B" to "whatever-file"
+          ),
+
+          listOf(
+            "not-important-dir-A" to "whatever-file",
+            "not-important-dir-B" to "whatever-file",
+            COMMUNITY_KOTLIN_PLUGIN to "File.kt"
+          )
+        )
+      }
+    }
+
+    @Parameter
+    lateinit var files: List<Pair<String, String>>
+
+    @Test
+    fun testThatChecksForFileSet() {
+      val filesSet = files.map { fileAt(it.first, it.second) }
+      assert(YouTrackIssueCommitMessageHandler.selectedFilesBelongToKotlinIdePlugin(filesSet)) {
+        "The following set of files doesn't trigger the check: $filesSet"
+      }
+    }
+  }
+
+
+  @RunWith(Parameterized::class)
+  class FilesDoNotBelongToPlugin {
+    companion object {
+      @JvmStatic
+      @Parameterized.Parameters(name = "{0}")
+      fun provideTestParameters(): Iterable<List<Pair<String, String>>> {
+        return listOf(
+          // file path has no kotlin-plugin subdirectory
+          listOf("not-important-dir" to "File.kt"),
+          listOf(FLEET_KOTLIN_PLUGIN to "File.kt"),
+
+          // kotlin-plugin path contains subdirectories to exclude
+          listOf("$ULTIMATE_KOTLIN_PLUGIN/test/" to "File.kt"),
+          listOf("$ULTIMATE_KOTLIN_PLUGIN/testData/" to "File.kt"),
+
+          // file extensions to exclude
+          listOf(COMMUNITY_KOTLIN_PLUGIN to "File.iml"),
+          listOf(COMMUNITY_KOTLIN_PLUGIN to "File.md"),
+
+          // multiple files, none matches
+          listOf(
+            "not-important-dir" to "File.kt",
+            FLEET_KOTLIN_PLUGIN to "File.kt",
+            "$ULTIMATE_KOTLIN_PLUGIN/test/" to "File.kt",
+            "$ULTIMATE_KOTLIN_PLUGIN/testData/" to "File.kt",
+            COMMUNITY_KOTLIN_PLUGIN to "File.iml",
+            COMMUNITY_KOTLIN_PLUGIN to "File.md"
+          )
+        )
+      }
+    }
+
+    @Parameter
+    lateinit var files: List<Pair<String, String>>
+
+    @Test
+    fun testThatIgnoresFileSet() {
+      val filesSet = files.map { fileAt(it.first, it.second) }
+      assert(!YouTrackIssueCommitMessageHandler.selectedFilesBelongToKotlinIdePlugin(filesSet)) {
+        "The following set of files triggered the check: $filesSet"
+      }
+    }
+  }
+
+  @RunWith(Parameterized::class)
+  class ValidCommitMessages {
+
+    companion object {
+      @JvmStatic
+      @Parameterized.Parameters(name = "{0}")
+      fun provideTestParameters(): Iterable<String> {
+        return listOf(
+          "KTIJ-123",
+          "(KTIJ-123)",
+          "[KTIJ-123]",
+          "{KTIJ-123}",
+          "'KTIJ-123'",
+          "`KTIJ-123`",
+          "\"KTIJ-123\"",
+
+          "KTIJ-123  ",
+          "  KTIJ-123",
+          "  KTIJ-123  ",
+
+          "KTIJ-123 header",
+          "Header KTIJ-123",
+          "Header KTIJ-123 header",
+
+          """
+            Header KTIJ-123 header
+            
+            Body-line-1
+            Body-line-N
+          """.trimIndent(),
+
+          """
+            Header KTIJ-123 header
+            
+            Body-line-1
+            Body-line-N
+
+            ^KTIJ-123 fixed
+          """.trimIndent(),
+
+          """
+            Header
+            
+            Body-line-1
+            Body-line-N
+
+            ^KTIJ-123 fixed
+          """.trimIndent(),
+
+          """
+            Header
+            
+            Body-line-1
+            Body-line-N
+
+            #KTIJ-123 fixed
+          """.trimIndent(),
+
+          """
+            Header
+            
+            Body-line-1
+            Body-line-N
+
+            Relates to #KTIJ-123
+          """.trimIndent()
+        )
+      }
+    }
+
+    @Parameter
+    lateinit var commitMessage: String
+
+    @Test
+    fun testThatCommitMessageIsValid() {
+      assert(YouTrackIssueCommitMessageHandler.commitMessageIsCorrect(commitMessage)) {
+        "The following commit message was considered invalid: $commitMessage"
+      }
+    }
+  }
+
+  @RunWith(Parameterized::class)
+  class InvalidCommitMessages {
+
+    companion object {
+      @JvmStatic
+      @Parameterized.Parameters(name = "{0}")
+      fun provideTestParameters(): Iterable<String> {
+        return listOf(
+          "",
+          "KTIJ",
+          "KTIJ-",
+          "KTIJ-one",
+          "KT-123",
+          "IDEA-123",
+          "WHATEVER-123",
+          "Header KTIJ",
+          "Header KTIJ header",
+
+          """
+            Header
+            
+            Body-line-1
+            Body-line-N
+          """.trimIndent(),
+
+          """
+            Header
+            
+            Body-line-1
+            Body-line-N
+            
+            ^IDEA-123 fixed
+          """.trimIndent(),
+
+          """
+            Header
+            
+            Body-line-1
+            Body-line-N
+            
+            #IDEA-123 fixed
+          """.trimIndent(),
+
+          """
+            Header
+            
+            Body-line-1
+            Body-line-N
+            
+            Relates to #IDEA-123
+          """.trimIndent(),
+        )
+      }
+    }
+
+    @Parameter
+    lateinit var commitMessage: String
+
+    @Test
+    fun testThatCommitMessageIsValid() {
+      assert(!YouTrackIssueCommitMessageHandler.commitMessageIsCorrect(commitMessage)) {
+        "The following commit message was considered as valid: $commitMessage"
+      }
+    }
+  }
+}
+
+
+val tempDir: String = System.getProperty("java.io.tmpdir")
+const val ULTIMATE_KOTLIN_PLUGIN = "plugins/kotlin/package/"
+const val COMMUNITY_KOTLIN_PLUGIN = "community/plugins/kotlin/package/"
+const val FLEET_KOTLIN_PLUGIN = "fleet/plugins/kotlin/package/"
+
+
+private fun fileAt(dirPath: String, fileName: String): File {
+  return Paths.get(tempDir, *dirPath.split("/").toTypedArray(), fileName).toFile()
+}
\ No newline at end of file