Add CloseableFakeSftpServer extends FakeSftpServer

[kriegaex]

The class can be instantiated, configured and closed manually, if doing everything within a single lambda expression is undesirable for a given use case. In order to achieve that, some methods and fields had to be made protected (from final).

For example, in BDD (behaviour-driven development) users want to test in a given-when-then fashion, i.e. separate the stimulus to the system under test (when) from verifying results later (then). Some test frameworks like Spock even require separate blocks, making the use of a single lambda feel somewhat unnatural and clunky there. See also this Stack Overflow answer.

Because the class implements AutoCloseable, it can be optionally also be instantiated in a try with resources structure.

A parametrised Spock (Groovy) example test looks like this:

class MySFTPServerTest extends Specification {
  @AutoCleanup
  def server = new CloseableFakeSftpServer()

  @Unroll("user #user downloads file #file")
  def "users can download text files"() {
    given: "a preconfigured fake SFTP server"
    server.addUser(user, password)
    server.putFile(file, content, UTF_8)

    and: "an SFTP client under test"
    def client = new SFTPFileDownloader("localhost", server.port, user, password)

    expect:
    client.getFileContent(file) == content

    where:
    user    | password | file                   | content
    "me"    | "xoxox"  | "/a/b/c/one.txt"       | "First line\nSecondLine\n"
    "you"   | "mypass" | "/etc/two.xml"         | "<root><foo>abc</foo></root>"
    "admin" | "secret" | "/home/admin/three.sh" | "#!/usr/bin/bash\n\nls -al\n"
  }
}

With the original FakeSftpServer, everything that is now cleanly separated by concern in the given:, and:, expect: blocks would be done within a single lambda expression, only for the sake of resource management, which is now handled via @AutoCleanup for the server field definition. As an alternative, in other test frameworks, server.close() could be called in a tear-down method running after the test or by using try with resources within the test.

[kriegaex]

With regard to the Maven build, I want to mention that even before my changes, several tests were failing. The exact same tests are failing now, i.e. I did not break anything in the base class.

Now Findbugs also complains about the FakeSftpServer.server being used in 3 places without null checks. This is not really relevant, so I did not address it but simply built with mvn -DskipTests -Dfindbugs.failOnError=false install and tested from my Spock project.