# Writing a Jenkins Shared Library pipeline
# The General Approach
First a quick run-down on how we build our library and on why we do it that way:
We will keep the “custom” steps inside var as simple as possible and without any real logic. Instead, we create classes (inside src) that do all the work.
We create an interface, which declares methods for all required Jenkins steps (sh, bat, error, etc.). The classes call steps only through this interface.
We write unit tests for your classes like you normally would with JUnit and Mockito. This way we are able to:
- Compile and execute our library/unit tests without Jenkins
- Test that our classes work as intended
- Test that Jenkins steps are called with the right parameters
- Test the behaviour of our code when a Jenkins step fails
- Build, test, run metrics and deploy your Jenkins Pipeline Library through Jenkins itself
Now let’s get really going.
# The Interface For Step Access
First, we will create the interface inside org.somecompany that will
be used by all classes to access the regular Jenkins steps like sh or
error. We will start with a simple example, and then I will provide a
more advanced one.
package org.somecompany
interface IStepExecutor {
int sh(String command)
void error(String message)
// add more methods for respective steps if needed
}
This interface is neat, because it can be mocked inside our unit tests. That way our classes become independent to Jenkins itself. For now, let’s add an implementation that will be used in our vars Groovy scripts:
package org.somecompany
class StepExecutor implements IStepExecutor {
// this will be provided by the vars script and
// let's us access Jenkins steps
private steps
StepExecutor(steps) {
this.steps = steps
}
@Override
int sh(String command) {
this.steps.sh returnStatus: true, script: "${command}"
}
@Override
void error(String message) {
this.steps.error(message)
}
}
Here is a more complex example, with more available methods. You can
expand on this by looking at the pipeline.gdsl file and taking
abstractions from there, both for methods, and properties.
import org.jenkinsci.plugins.workflow.cps.EnvActionImpl
import org.jenkinsci.plugins.workflow.support.steps.build.RunWrapper
interface IStepExecutor {
/**
* Current build environment variables
*/
public EnvActionImpl env
/**
* Current build details
*/
public RunWrapper currentBuild
/**
* Current build parameters
*/
public Map params
/**
* Shell Script
* @param command
* @return
*/
int sh(String command)
/**
* Shell Script
* @param label
* @param command
* @return
*/
int sh(String label, String command)
/**
* Error signal
* @param message
*/
void error(String message)
/**
* Stage of a Jenkins build
* @param name
* @param body
*/
void stage(String name, Closure body)
/**
* Execute closures in parallel
* @param closures
*/
void parallel(Map closures)
/**
* Recursively delete the current directory from the workspace
*/
void deleteDir()
/**
* Update the commit status in GitHub
* @param name
* @param status
*/
void updateGitlabCommitStatus(String name, String status)
/**
* Send Slack Message
* @param channel
* @param color
* @param iconEmoji
* @param message
*/
void slackSend(String channel, String color, String iconEmoji, String message)
/**
* Accept GitHub Merge Request
* @param useMRDescription
* @param removeSourceBranch
*/
void acceptGitHubMR(Boolean useMRDescription, Boolean removeSourceBranch)
/**
* Archive JUnit-formatted test results
* @param location
*/
void junit(String location)
/**
* Stash some files to be used later in the build
* @param name
* @param includes
*/
void stash(String name, String includes)
/**
* Restore files previously stashed
* @param name
*/
void unstash(String name)
/**
* PowerShell Script
* @param command
* @return
*/
int powershell(String command)
/**
* PowerShell Script
* @param label
* @param command
* @return
*/
int powershell(String label, String command)
/**
* Change current directory
* @param directory
* @param body
*/
void dir(String directory, Closure body)
/**
* Allocate node. Change execution of build to said agent
* @param name
* @param body
*/
void node(String name, Closure body)
/**
* Catch error and set build result to failure
* @param params
* @param body
*/
void catchError(Map params, Closure body)
/**
* Add Cobertura coverage report result
* @param location
*/
void cobertura(String location)
}
And the implementation:
import org.jenkinsci.plugins.workflow.cps.EnvActionImpl
import org.jenkinsci.plugins.workflow.support.steps.build.RunWrapper
final class StepExecutor implements IStepExecutor {
// this will be provided by the vars script and
// let's us access Jenkins steps
private steps
public EnvActionImpl env
public RunWrapper currentBuild
public Map params
StepExecutor(steps) {
this.steps = steps
this.env = this.steps.env
this.currentBuild = this.steps.currentBuild
this.params = Collections.unmodifiableMap(this.steps.params)
}
@Override
int sh(String command) {
this.steps.sh returnStatus: true, script: "${command}"
}
@Override
int sh(String description, String command) {
this.steps.sh returnStatus: true, label: "${description}", script: "${command}"
}
@Override
int powershell(String command) {
this.steps.powershell returnStatus: true, script: "${command}"
}
@Override
int powershell(String description, String command) {
this.steps.powershell returnStatus: true, label: "${description}", script: "${command}"
}
@Override
void error(String message) {
this.steps.currentBuild.setResult(JobStatus.Failure)
this.steps.error(message)
}
@Override
void stage(String name, Closure body) {
this.steps.stage(name, body)
}
@Override
void parallel(Map closures) {
this.steps.parallel(closures)
}
@Override
void deleteDir() {
this.steps.deleteDir()
}
@Override
void updateGitlabCommitStatus(String name, String status) {
this.steps.updateGitlabCommitStatus name: "${name}", status: "${status}"
}
@Override
void slackSend(String channel, String color, String iconEmoji, String message) {
this.steps.slackSend baseUrl: "https://hooks.slack.com/services/", botUser: true,
channel: "${channel}", color: "${color}", iconEmoji: "${iconEmoji}",
message: "${message}", teamDomain: "teamDomain",
tokenCredentialId: "token", username: "webhookbot"
}
@Override
void acceptGitHubMR(Boolean useMRDescription, Boolean removeSourceBranch) {
this.steps.acceptGitHubMR useMRDescription: useMRDescription, removeSourceBranch: removeSourceBranch
}
@Override
void stash(String name, String includes) {
this.steps.stash name: "${name}", includes: "${includes}"
}
@Override
void unstash(String name) {
this.steps.unstash name: "${name}"
}
@Override
void dir(String directory, Closure body) {
this.steps.dir(directory, body)
}
@Override
void node(String name, Closure body) {
this.steps.node(name, body)
}
@Override
void catchError(Map params, Closure body) {
this.steps.catchError buildResult: params.buildResult,
catchInterruptions: params.catchInterruptions,
message: params.message,
stageResult: params.stageResult,
body: body
}
@Override
void junit(String location) {
this.steps.junit testResults: "${location}", allowEmptyResults: false
}
@Override
void cobertura(String location) {
this.steps.cobertura autoUpdateHealth: false,
autoUpdateStability: false,
coberturaReportFile: "${location}",
conditionalCoverageTargets: '70, 0, 0',
failUnhealthy: false,
failUnstable: false,
lineCoverageTargets: '80, 0, 0',
maxNumberOfBuilds: 0,
methodCoverageTargets: '80, 0, 0',
onlyStable: false,
sourceEncoding: 'ASCII',
zoomCoverageChart: false
}
}
# Adding Basic Dependency Injection
Because we don’t want to use the above implementation in our unit tests, we will setup some basic dependency injection in order to swap the above implementation with a mock during unit tests. If you are not familiar with dependency injection, you should probably read up about it, since explaining it here would be out-of-scope, but you might be fine with just copy-pasting the code in this chapter and follow along.
So, first we create the org.somecompany.ioc package and add an IContext interface:
package org.somecompany.ioc
import org.somecompany.IStepExecutor
interface IContext {
IStepExecutor getStepExecutor()
}
Again, this interface will be mocked for our unit tests. But for regular execution of our library we still need an default implementation:
package org.somecompany.ioc
import org.somecompany.IStepExecutor
import org.somecompany.StepExecutor
class DefaultContext implements IContext, Serializable {
// the same as in the StepExecutor class
private steps
DefaultContext(steps) {
this.steps = steps
}
@Override
IStepExecutor getStepExecutor() {
return new StepExecutor(this.steps)
}
}
To finish up our basic dependency injection setup, let’s add a “context registry” that is used to store the current context (DefaultContext during normal execution and a Mockito mock of IContext during unit tests):
package org.somecompany.ioc
class ContextRegistry implements Serializable {
private static IContext context
static void registerContext(IContext context) {
context = context
}
static void registerDefaultContext(Object steps) {
context = new DefaultContext(steps)
}
static IContext getContext() {
return context
}
}
That’s it! Now we are free to code testable Jenkins steps inside vars.
# Coding A Custom Jenkins Step
Let’s imagine for our example here, that we want to add a step to our
library that calls the some class that performs some data seeding to a
database. To do this we first add a groovy script example_build.groovy
to the vars folder that is called like our custom step we want to
implement. Since our script is called example_build.groovy our step
will later be callable with example_build in our Jenkinsfile. Add
the following content to the script for now:
void call(
String environment,
String envFile,
String dataSeederBranch,
String deploymentScriptsBranch
) {
// TODO
}
According to our general idea we want to keep our example_build script
as simple as possible and do all the work inside a unit-testable class.
So let’s create a new class DataSeederJob in a new package
org.somecompany.jobs:
package org.somecompany.jobs
final class DataSeederJob implements Serializable {
private String workspace
private String environment
private String envFile
private String dataSeederBranch
private String deploymentScriptsBranch
private String seedingEnvironment
private String seedingMode
private ArrayList<TargetRepository> repositories
DataSeederJob(
String workspace,
String environment,
String envFile,
String dataSeederBranch,
String deploymentScriptsBranch,
String seedingEnvironment,
String seedingMode
) {
this.workspace = workspace
this.environment = environment
this.envFile = envFile
this.dataSeederBranch = dataSeederBranch
this.deploymentScriptsBranch = deploymentScriptsBranch
this.seedingEnvironment = seedingEnvironment
this.seedingMode = seedingMode
this.repositories = [
new TargetRepository(
"repo1",
this.deploymentScriptsBranch,
"deploymentscripts"
),
new TargetRepository(
"repo2",
this.dataSeederBranch,
"dataseeder"
)
]
}
void build() {
IStepExecutor steps = ContextRegistry.getContext().getStepExecutor()
steps.deleteDir()
steps.stage("Cloning new content", {
SourceControlUtils.parallelCheckoutCode(steps, this.repositories)
})
steps.stage("Preparing application environment", {
int status = steps.sh("""
/bin/cp deploymentscripts/${this.environment}/DataSeeder/${this.envFile} dataseeder/dist/config.toml
""")
if (status != 0) {
steps.error("Job failed! Copying env file exited with a non-zero status!")
}
})
steps.stage("Running DataSeeder", {
int status = steps.sh("""
cd dataseeder/dist
./goseeders-linux-x86 -env=${this.seedingEnvironment} -mode=${this.seedingMode}
""")
if (status != 0) {
steps.error("Job failed! Application exited with a non-zero status!")
}
})
}
}
As you can see, we use both the sh, deleteDir, stage and error steps in our class, but instead of using them directly, we use the ContextRegistry to get an instance of IStepExecutor to call Jenkins steps with that. This way, we can swap out the context when we want to unit test the build() method later.
Now we can finish our script in vars folder, which in this case will
also send a Slack message on failure:
void call(
String environment,
String envFile,
String dataSeederBranch,
String deploymentScriptsBranch
) {
ContextRegistry.registerDefaultContext(this)
IStepExecutor steps = ContextRegistry.getContext().getStepExecutor()
try {
DataSeederJob buildExecutor = new DataSeederJob(
steps.env.getProperty(EnvironmentVariables.workspace),
environment,
envFile,
dataSeederBranch,
deploymentScriptsBranch,
steps.params["SeedingEnvironment"] as String,
steps.params["SeedingMode"] as String
)
buildExecutor.build()
} catch (e) {
steps.currentBuild.setResult(JobStatus.Failure)
throw e
} finally {
String result = JobStatus.Success
if (steps.currentBuild.getResult() != null) {
result = steps.currentBuild.getResult()
}
switch (result) {
case JobStatus.Failure:
steps.slackSend(
SlackChannels.monitoringChannel,
SlackColors.failure,
SlackEmojis.failure,
String.format("""
%s - TEST PIPELINE FRAMEWORK
PARAMETERS: %s
""",
steps.currentBuild.getFullDisplayName(),
steps.params.toString(),
),
)
break
default:
break
}
}
}
First, we set the context with the context registry. Since we are not in
a unit test, we use the default context. The this that gets passed
into registerDefaultContext() will be saved by the DefaultContext
inside its private steps variable and is used to access Jenkins steps.
After registering the context, we are free to instantiate our MsBuild
class and call the build() method doing all the work.
Nice, our vars script is finished. Now we only have to write some unit
tests for our Job class.
# Adding Unit Tests
At this point writing unit tests should be business as usual. We create
a new test class JobTest inside the test folder with package
org.somecompany.jobs. Before every test, we use Mockito to mock the
IContext and IStepExecutor interfaces and register the mocked
context. Then we can simply create a new Job instance in our test and
verify the behaviour of our build() method.
Here is the data seeder test class:
import org.junit.jupiter.api.BeforeEach
import org.junit.jupiter.api.Test
import static org.mockito.ArgumentMatchers.any
import static org.mockito.ArgumentMatchers.anyString
import static org.mockito.Mockito.times
import static org.mockito.Mockito.verify
final class DataSeederJobTest {
private DataSeederJob sut
protected IContext context
protected IStepExecutor steps
@BeforeEach
void setup() {
context = mock(IContext.class)
steps = mock(IStepExecutor.class)
when(context.getStepExecutor()).thenReturn(steps)
ContextRegistry.registerContext(context)
}
@BeforeEach
void setupJob() {
String workspace = "workspace"
String environment = "environment"
String envFile = "envFile"
String dataSeederBranch = "dataSeederBranch"
String deploymentScriptsBranch = "deploymentScriptsBranch"
String seedingEnvironment = "seedingEnvironment"
String seedingMode = "seedingMode"
this.sut = new DataSeederJob(
workspace,
environment,
envFile,
dataSeederBranch,
deploymentScriptsBranch,
seedingEnvironment,
seedingMode
)
}
@Test
void jobBuildCallsDeleteDirStep() {
this.sut.build()
verify(steps).deleteDir()
}
@Test
void jobBuildCallsStageSteps() {
this.sut.build()
verify(steps, times(3)).stage(anyString(), any(Closure))
}
}
Another test class with several example tests, but unrelated to the data seeder:
package org.somecompany.jobs
import org.junit.jupiter.api.BeforeEach
import org.junit.jupiter.api.Test
import static org.mockito.ArgumentMatchers.any
import static org.mockito.ArgumentMatchers.anyString
import static org.mockito.Mockito.*
import org.junit.jupiter.api.BeforeEach
import static org.mockito.Mockito.mock
import static org.mockito.Mockito.when
final class GenericGoJobTest {
private GenericGoJob sut
private String workspace = "workspace"
private String appName = "appName"
private String releaseDir = "releaseDir"
private String repoName = "repoName"
private String serviceName = "serviceName"
private Boolean shouldUnitTest = false
private Boolean deployToDifferentAgents = false
private ArrayList<String> destinationAgents = ["destinationAgent"]
private String mainGoFileLocation = "mainGoFileLocation"
protected IContext context
protected IStepExecutor steps
@BeforeEach
void setup() {
context = mock(IContext.class)
steps = mock(IStepExecutor.class)
when(context.getStepExecutor()).thenReturn(steps)
ContextRegistry.registerContext(context)
}
@BeforeEach
void setupJob() {
this.sut = new GenericGoJob(
this.workspace,
this.appName,
this.releaseDir,
this.repoName,
this.serviceName,
this.mainGoFileLocation,
this.shouldUnitTest,
this.deployToDifferentAgents,
this.destinationAgents,
)
}
@Test
void verifyJobCallsDeleteDir() {
this.sut.build()
verify(steps).deleteDir()
}
@Test
void verifyJobCallsStagesCorrectAmountOfTimes() {
this.sut.build()
verify(steps, times(5)).stage(anyString(), any(Closure))
}
@Test
void verifyJobCallsStagesCorrectAmountOfTimesWithDifferentAgentOption() {
this.deployToDifferentAgents = true
this.setupJob()
this.sut.build()
verify(steps, times(4)).stage(anyString(), any(Closure))
}
@Test
void verifyJobDoesNotCallNode() {
this.sut.build()
verify(steps, times(0)).node(anyString(), any(Closure))
}
@Test
void verifyJobCallsNodeWithDifferentAgentOption() {
this.deployToDifferentAgents = true
this.setupJob()
this.sut.build()
verify(steps, times(1)).node(anyString(), any(Closure))
}
@Test
void verifyJobCallsStageOneMoreTimeWithUnitTests() {
this.shouldUnitTest = true
this.setupJob()
this.sut.build()
verify(steps, times(6)).stage(anyString(), any(Closure))
}
@Test
void verifyJobCallsNodeMultipleTimesWithDifferentAgentOption() {
this.deployToDifferentAgents = true
this.destinationAgents = [
"test1",
"test2",
"test3",
"test4",
"test5",
]
this.setupJob()
this.sut.build()
verify(steps, times(5)).node(anyString(), any(Closure))
}
@Test
void verifyDeployGoSystemServiceCallsDir() {
this.sut.deployGoSystemService(steps)
verify(steps, times(1)).dir(anyString(), any(Closure))
}
@Test
void verifyBuildGoApplicationCallsSh() {
this.sut.buildGoApplication(steps)
verify(steps, times(1)).sh(anyString())
}
@Test
void verifyBuildGoApplicationCallsError() {
when(steps.sh(anyString())).thenReturn(-1)
this.sut.buildGoApplication(steps)
verify(steps).error(anyString())
}
@Test
void verifyUnitTestApplicationCallsStage() {
this.sut.unitTestApplication(steps)
verify(steps, times(1)).stage(anyString(), any(Closure))
}
@Test
void verifyDeployBuildCallsNodeCorrectly() {
this.deployToDifferentAgents = true
this.destinationAgents = [
"test1",
"test2",
"test3",
"test4",
"test5",
]
this.setupJob()
this.sut.deployBuild(steps)
verify(steps, times(5)).node(anyString(), any(Closure))
}
@Test
void verifyDeployBuildCallsStageCorrect() {
this.sut.deployBuild(steps)
verify(steps, times(1)).stage(anyString(), any(Closure))
}
@Test
void verifyPrepareStashContentCallsSh() {
this.sut.prepareStashContent(steps)
verify(steps, times(2)).sh(anyString())
}
@Test
void verifyPrepareStashCallsError() {
when(steps.sh(anyString())).thenReturn(-1)
this.sut.prepareStashContent(steps)
verify(steps, times(2)).error(anyString())
}
@Test
void verifyStashBuildCallsSh() {
this.sut.stashBuild(steps)
verify(steps, times(1)).sh(anyString())
}
@Test
void verifyStashBuildCallsError() {
when(steps.sh(anyString())).thenReturn(-1)
this.sut.stashBuild(steps)
verify(steps).error(anyString())
}
}
You can use the green play buttons on left of the IntelliJ code editor to run the tests, which hopefully turn green.
# Wrapping Things Up
That’s basically it. Now it’s time to setup your library with Jenkins,
create a new job and run a Jenkinsfile to test your new custom
example_build step. A simple test Jenkinsfile could look like this:
node('master') {
// Load your library
library('pipeline-framework@master')
// call the script with parameters
// if your call function does not require any params
// you could simply do example_build.call(), which I prefer,
// or simply example_build
example_build.call(
'Acceptance',
'config.toml',
'master',
'stable'
)
}
Then you can decide either to add this to a Pipeline job immediately on the script box, or checkout this small script from SCM, that is up to you.
Obviously there is still a lot more I could have talked about (things like unit tests, dependency injection, Gradle, Jenkins configuration, build and testing the library with Jenkins itself etc.), but I wanted to keep this already very long blog post somewhat concise. I do hope however, that the general idea and approach became clear and helps you in creating a unit-testable shared library, that is more robust and easier to work on than it normally would be.
One last piece of advice: The unit tests and Gradle setup are pretty nice and help a ton in easing the development of robust shared pipelines, but unfortunately there is still quite a bit that can go wrong inside your pipelines even though the library tests are green. Things like the following, that mostly happen because of Jenkins’ Groovy and sandbox weirdness:
- A class that does not implement Serializable which is necessary, because “pipelines must survive Jenkins restarts”
- Using classes like java.io.File inside your library, which is prohibited
- Syntax and spelling errors in your
Jenkinsfile
Therefore, it might be a good idea to have Jenkins instance solely for
integration testing, where new and modified vars scripts can be tested
before going “live”.
Again, feel free to write any kind of questions or feedback in the comments, or contact me directly.