Parallel test execution in Jenkins - Step-by-Step Execution

Process Flow - Parallel test execution

Start Jenkins Pipeline

↓

Define parallel stages

↓

Trigger tests in parallel

↓

Wait for all tests to finish

↓

Collect and report results

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End

The Jenkins pipeline starts, defines multiple test stages to run at the same time, waits for all to finish, then collects results.

Execution Sample

Jenkins

pipeline {
  agent any
  stages {
    stage('Parallel Tests') {
      parallel {
        'Test A': {
          steps { echo 'Running Test A' }
        },
        'Test B': {
          steps { echo 'Running Test B' }
        }
      }
    }
  }
}

This Jenkins pipeline runs two test stages, Test A and Test B, at the same time.

Process Table

Step	Action	Stage Running	Output	Notes
1	Start pipeline	None	Pipeline started	Pipeline begins execution
2	Enter 'Parallel Tests' stage	None	Entering parallel block	Prepare to run parallel stages
3	Start 'Test A' stage	Test A	Running Test A	Test A runs independently
4	Start 'Test B' stage	Test B	Running Test B	Test B runs independently
5	Wait for 'Test A' and 'Test B' to finish	Test A, Test B	Both tests complete	Parallel stages complete
6	Collect results	None	Results collected	Pipeline gathers test outputs
7	End pipeline	None	Pipeline finished	Pipeline execution ends

💡 All parallel test stages complete, pipeline finishes.

Status Tracker

Variable	Start	After Step 3	After Step 4	After Step 5	Final
Stage Running	None	Test A	Test A, Test B	None	None
Output	Pipeline started	Running Test A	Running Test A, Running Test B	Both tests complete	Pipeline finished

Key Moments - 2 Insights

Why do 'Test A' and 'Test B' run at the same time instead of one after the other?

Because they are defined inside the 'parallel' block (see execution_table steps 3 and 4), Jenkins runs these stages simultaneously to save time.

What happens if one parallel test fails?

The pipeline waits for all parallel stages to finish (step 5), but the overall pipeline may fail depending on the test results. This ensures all tests complete before reporting.

Visual Quiz - 3 Questions

Look at the execution table, at which step do both 'Test A' and 'Test B' run simultaneously?

A Step 4

B Step 2

C Step 3

D Step 5

💡 Hint

Check the 'Stage Running' column in steps 3 and 4 to see when both tests are active.

According to the variable tracker, what is the value of 'Stage Running' after step 4?

A None

B Test A

C Test A, Test B

D Test B

💡 Hint

Look at the 'Stage Running' row in variable_tracker after step 4.

If we remove the 'parallel' block and run tests sequentially, how would the execution table change?

A There would be no 'Parallel Tests' stage.

B Steps 3 and 4 would run one after another, not simultaneously.

C Steps 3 and 4 would still run at the same time.

D The pipeline would skip tests.

💡 Hint

Parallel block controls simultaneous execution; removing it causes sequential runs.

Concept Snapshot

Jenkins Parallel Test Execution:
- Use 'parallel' block inside a stage to run multiple tests at once.
- Each test runs independently, saving time.
- Pipeline waits for all parallel tests to finish before continuing.
- Useful for speeding up test suites in CI pipelines.

Full Transcript

This visual execution shows how Jenkins runs tests in parallel. The pipeline starts, then enters a stage with a parallel block. Inside, Test A and Test B start at the same time. Jenkins waits for both to finish, then collects results and ends the pipeline. Variables track which stages run and outputs at each step. Key points include understanding that parallel stages run simultaneously and the pipeline waits for all to complete before moving on. The quiz checks understanding of when tests run together and how removing parallel changes execution.