Bats Testing Patterns

Comprehensive guidance for writing comprehensive unit tests for shell scripts using Bats (Bash Automated Testing System), including test patterns, fixtures, and best practices for production-grade shell testing.

When to Use This Skill

Writing unit tests for shell scripts
Implementing test-driven development (TDD) for scripts
Setting up automated testing in CI/CD pipelines
Testing edge cases and error conditions
Validating behavior across different shell environments
Building maintainable test suites for scripts
Creating fixtures for complex test scenarios
Testing multiple shell dialects (bash, sh, dash)

Detailed patterns and worked examples

Detailed pattern documentation lives in references/details.md. Read that file when the navigation tier above is insufficient.

Testing Error Conditions

bash

#!/usr/bin/env bats

@test "Function fails with missing file" {
    run my_function "/nonexistent/file.txt"
    [ "$status" -ne 0 ]
    [[ "$output" == *"not found"* ]]
}

@test "Function fails with invalid input" {
    run my_function ""
    [ "$status" -ne 0 ]
}

@test "Function fails with permission denied" {
    touch "$TMPDIR/readonly.txt"
    chmod 000 "$TMPDIR/readonly.txt"
    run my_function "$TMPDIR/readonly.txt"
    [ "$status" -ne 0 ]
    chmod 644 "$TMPDIR/readonly.txt"  # Cleanup
}

@test "Function provides helpful error message" {
    run my_function --invalid-option
    [ "$status" -ne 0 ]
    [[ "$output" == *"Usage:"* ]]
}

Testing with Dependencies

bash

#!/usr/bin/env bats

setup() {
    # Check for required tools
    if ! command -v jq &>/dev/null; then
        skip "jq is not installed"
    fi

    export SCRIPT="${BATS_TEST_DIRNAME}/../bin/script.sh"
}

@test "JSON parsing works" {
    skip_if ! command -v jq &>/dev/null
    run my_json_parser '{"key": "value"}'
    [ "$status" -eq 0 ]
}

Testing Shell Compatibility

bash

#!/usr/bin/env bats

@test "Script works in bash" {
    bash "${BATS_TEST_DIRNAME}/../bin/script.sh" arg1
}

@test "Script works in sh (POSIX)" {
    sh "${BATS_TEST_DIRNAME}/../bin/script.sh" arg1
}

@test "Script works in dash" {
    if command -v dash &>/dev/null; then
        dash "${BATS_TEST_DIRNAME}/../bin/script.sh" arg1
    else
        skip "dash not installed"
    fi
}

Parallel Execution

bash

#!/usr/bin/env bats

@test "Multiple independent operations" {
    run bash -c 'for i in {1..10}; do
        my_operation "$i" &
    done
    wait'
    [ "$status" -eq 0 ]
}

@test "Concurrent file operations" {
    for i in {1..5}; do
        my_function "$TMPDIR/file$i" &
    done
    wait
    [ -f "$TMPDIR/file1" ]
    [ -f "$TMPDIR/file5" ]
}

Test Helper Pattern

test_helper.sh

bash

#!/usr/bin/env bash

# Source script under test
export SCRIPT_DIR="${BATS_TEST_DIRNAME%/*}/bin"

# Common test utilities
assert_file_exists() {
    if [ ! -f "\$1" ]; then
        echo "Expected file to exist: \$1"
        return 1
    fi
}

assert_file_equals() {
    local file="\$1"
    local expected="\$2"

    if [ ! -f "$file" ]; then
        echo "File does not exist: $file"
        return 1
    fi

    local actual=$(cat "$file")
    if [ "$actual" != "$expected" ]; then
        echo "File contents do not match"
        echo "Expected: $expected"
        echo "Actual: $actual"
        return 1
    fi
}

# Create temporary test directory
setup_test_dir() {
    export TEST_DIR=$(mktemp -d)
}

cleanup_test_dir() {
    rm -rf "$TEST_DIR"
}

Integration with CI/CD

GitHub Actions Workflow

yaml

name: Tests

on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v3

      - name: Install Bats
        run: |
          npm install --global bats

      - name: Run Tests
        run: |
          bats tests/*.bats

      - name: Run Tests with Tap Reporter
        run: |
          bats tests/*.bats --tap | tee test_output.tap

Makefile Integration

makefile

.PHONY: test test-verbose test-tap

test:
	bats tests/*.bats

test-verbose:
	bats tests/*.bats --verbose

test-tap:
	bats tests/*.bats --tap

test-parallel:
	bats tests/*.bats --parallel 4

coverage: test
	# Optional: Generate coverage reports

Best Practices

Test one thing per test - Single responsibility principle
Use descriptive test names - Clearly states what is being tested
Clean up after tests - Always remove temporary files in teardown
Test both success and failure paths - Don't just test happy path
Mock external dependencies - Isolate unit under test
Use fixtures for complex data - Makes tests more readable
Run tests in CI/CD - Catch regressions early
Test across shell dialects - Ensure portability
Keep tests fast - Run in parallel when possible
Document complex test setup - Explain unusual patterns