How to use Spock for mocking slf4j?

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To use Spock for mocking slf4j, you can follow the below steps:

Step 1: Add Spock dependency in the build system (e.g. Gradle, Maven)

For Gradle:

testCompile 'org.spockframework:spock-core:x.x.x'

For Maven:

<dependency>
  <groupId>org.spockframework</groupId>
  <artifactId>spock-core</artifactId>
  <version>x.x.x</version>
  <scope>test</scope>
</dependency>

Step 2: Create a Spock specification

import ch.qos.logback.classic.Level
import ch.qos.logback.classic.Logger
import org.slf4j.LoggerFactory
import spock.lang.Specification

class MySpec extends Specification {
  def "my test"() {
    given:
    def logger = mock(LoggerFactory.getLogger("myLogger"), true)

    when:
    logger.warn("Warning message")

    then:
    1 * logger.warn("Warning message")
    logger.warn("Warning message") >> {}
    ReusedDependencyInjector.DEFAULT.verifyNoMoreInteractions()
  }
}

Note:

• The LoggerFactory is used to obtain a logger instance (by name). In this case, we're using the name myLogger.
• The mock function is used to create a mock instance of the desired class (in this case, Logger). The second argument specifies that we also want to mock the static methods of LoggerFactory.
• The 1 * logger.warn("Warning message") line specifies that we expect the warn method to be called once with the argument "Warning message".
• The logger.warn("Warning message") >> {} line specifies that we want the warn method to do nothing (i.e. return void).
• The ReusedDependencyInjector.DEFAULT.verifyNoMoreInteractions() line specifies that we want to verify that there are no other interactions with the mock object. This is useful for detecting unexpected calls to the mocked object.

Step 3: Run the Spock specification

Run the specification using your favorite test runner (e.g. IntelliJ IDEA, Gradle, Maven).

That's it! You now have a Spock specification that mocks slf4j.