Testing Bash Scripts With Bats in Linux

Bash Automated Testing System (BATS) is a testing framework designed specifically for bash scripts. It allows developers to write automated tests for their bash code, ensuring scripts function correctly before deployment and improving code reliability in production environments.

BATS provides a structured approach to testing bash scripts similar to testing frameworks available for other programming languages like Python or Java. It uses a simple syntax that makes writing and maintaining tests straightforward for shell script developers.

What is BATS?

BATS stands for Bash Automated Testing System. It is a TAP-compliant testing framework that runs tests written in bash syntax. The framework executes test cases and provides clear feedback about which tests pass or fail, making it easier to identify issues in bash scripts before they reach production.

Key features of BATS include

• Simple syntax Tests are written using familiar bash constructs

• Assertion helpers Built-in functions for common test scenarios

• Detailed output Clear reporting of test results and failures

• Integration support Works well with CI/CD pipelines

Setting Up BATS

First, ensure git is installed on your system

sudo apt update
sudo apt install git
git version

Initialize your project directory and install BATS with its helper libraries as git submodules

git init
git submodule add https://github.com/bats-core/bats-core.git test/bats
git submodule add https://github.com/bats-core/bats-support.git test/test_helper/bats-support
git submodule add https://github.com/bats-core/bats-assert.git test/test_helper/bats-assert
git submodule add https://github.com/bats-core/bats-file.git test/test_helper/bats-file

Creating a Sample Bash Script

Let's create a simple bash script to demonstrate testing. Create browser_choice.sh

#!/usr/bin/env bash

if [ $# -ne 3 ]; then
    echo "Usage: $0 <browser> <search_engine> <output_file>"
    exit 1
fi

choice="Web Browser $1 over $2"
echo "$choice"
echo "$choice" > "$3"
exit 0

Make the script executable

chmod +x browser_choice.sh

Writing BATS Tests

Create a test file test/browser_choice.bats

#!/usr/bin/env bats

load 'test_helper/bats-support/load'
load 'test_helper/bats-assert/load'

@test "script exists and is executable" {
    [ -x "./browser_choice.sh" ]
}

@test "script runs with correct arguments" {
    run ./browser_choice.sh firefox google output.txt
    assert_success
    assert_output "Web Browser firefox over google"
}

@test "script creates output file" {
    run ./browser_choice.sh chrome bing test_output.txt
    assert_success
    [ -f "test_output.txt" ]
    run cat test_output.txt
    assert_output "Web Browser chrome over bing"
    rm -f test_output.txt
}

@test "script fails with insufficient arguments" {
    run ./browser_choice.sh firefox
    assert_failure
    assert_output --partial "Usage:"
}

Running Tests

Execute the BATS tests from your project root directory

./test/bats/bin/bats test/browser_choice.bats

Expected output

browser_choice.bats
 ? script exists and is executable
 ? script runs with correct arguments  
 ? script creates output file
 ? script fails with insufficient arguments

4 tests, 0 failures

Common BATS Assertions

Conclusion

BATS provides a robust testing framework for bash scripts, bringing automated testing practices to shell scripting. It offers simple syntax for writing tests, comprehensive assertion helpers, and clear output reporting. By implementing BATS testing, developers can significantly improve the reliability and maintainability of their bash scripts.