Fail if the commit does not have CHANGELOG tag

build.gradle

dependencies {
  testImplementation 'org.eclipse.jgit:org.eclipse.jgit:5.2.0.201812061821-r'
}

CommitVerifier.kt

import org.eclipse.jgit.storage.file.FileRepositoryBuilder
import org.hamcrest.core.IsEqual
import org.junit.Assert
import org.junit.Test
import java.io.File
import java.util.*

class CommitVerifier {
  @Test
  fun changelogPresents() {
    val repository = FileRepositoryBuilder().setGitDir(File("../.git"))
      .setMustExist(true)
      .build()
    val currentCommit = repository.parseCommit(repository.resolve("HEAD"))
    if (currentCommit.parentCount == 1) { // not merge commit
      val currentMessage = currentCommit.fullMessage
      var wasChangeLogInfo = false
      Scanner(currentMessage).use { scanner ->
        while (scanner.hasNextLine()) {
          val line = scanner.nextLine()
          if (line.trimStart().startsWith("CHANGELOG:")) {
            wasChangeLogInfo = true
          }
        }
      }

      Assert.assertThat(
        "Your last commit does not have the CHANGELOG tag. Please, add it",
        wasChangeLogInfo,
        IsEqual.equalTo(true)
      )
    }
  }
}