threshold-plugin-aws/testing/testing.go

package testing

import (
	"encoding/json"
	"errors"
	"fmt"
	"os/exec"
	"sync"

	tfjson "github.com/hashicorp/terraform-json"
)

// TestTerraformer is an object representing the lifecycle of a
// particular Terraform project.
//
// Note that Terraform must be installed in the system PATH (not to
// be confused with the working directory below). This object does
// not manage anything with regards to installation or version
// management.
type TestTerraformer struct {
	// The full path to the Terraform binary, set during initialization
	// to the binary found in the system path.
	tfPath string

	// The working directory for Terraform commands.
	workDir string

	// The Terraform state. Use the Output method to look up particular
	// outputs from the Terraform state.
	state *tfjson.State

	// Keeps track of whether or not we have run the init command
	// during this run of Terraform. This only needs to be done once.
	// Do not use initErr directly; it stores the init error if one was
	// encountered on init.
	initOnce sync.Once
	initErr  error
}

// NewTestTerraformer initializes a Terraform directory. It just
// returns an initialized project, it does not perform any actions on
// it.
func NewTestTerraformer(workDir string) (*TestTerraformer, error) {
	tfPath, err := exec.LookPath("terraform")
	if err != nil {
		return nil, fmt.Errorf("LookPath error: %w", err)
	}

	if workDir == "" {
		return nil, errors.New("workDir is empty")
	}

	return &TestTerraformer{
		tfPath:  tfPath,
		workDir: workDir,
	}, nil
}

// Deploy runs the following commands, in order: init, apply, plan,
// json. The output of the JSON command is then imported to the
// internal state.
func (t *TestTerraformer) Deploy() error {
	if err := t.init(); err != nil {
		return fmt.Errorf("error running Terraform init: %w", err)
	}

	if err := t.apply(); err != nil {
		return fmt.Errorf("error running Terraform apply: %w", err)
	}

	if err := t.plan(); err != nil {
		return fmt.Errorf("error running Terraform plan: %w", err)
	}

	output, err := t.showJson()
	if err != nil {
		return fmt.Errorf("error getting Terraform plan JSON data: %w", err)
	}

	newState := new(tfjson.Plan)
	if err := json.Unmarshal(output, newState); err != nil {
		return fmt.Errorf("error reading new Terraform plan JSON data: %w", err)
	}

	t.state = newState.PriorState
	return nil
}

// Destroy runs the following commands, in order: init, destroy. The
// state is also cleared.
func (t *TestTerraformer) Destroy() error {
	if err := t.init(); err != nil {
		return fmt.Errorf("error running Terraform init: %w", err)
	}

	if err := t.destroy(); err != nil {
		return fmt.Errorf("error running Terraform destroy: %w", err)
	}

	t.state = nil
	return nil
}

// GetOutput returns the value of the output located at key.
//
// Outputs for the root module are supported only. It's an error to
// run this when no state exists.
func (t *TestTerraformer) GetOutput(key string) (interface{}, error) {
	if key == "" {
		return nil, errors.New("key must not be empty")
	}

	if t.state == nil {
		return nil, errors.New("state is nil")
	}

	if t.state.Values == nil {
		return nil, errors.New("state integrity error: no state values")
	}

	if t.state.Values.Outputs == nil {
		return nil, errors.New("state integrity error: outputs is nil")
	}

	output, ok := t.state.Values.Outputs[key]
	if !ok {
		return nil, fmt.Errorf("output with key %q not found", key)
	}

	if output == nil {
		return nil, fmt.Errorf("state integrity error: output at key %q is nil", key)
	}

	return output.Value, nil
}

// init runs "terraform init" in the project's working directory.
//
// This is only ever done once.
func (t *TestTerraformer) init() error {
	t.initOnce.Do(func() {
		cmd := exec.Command(t.tfPath, "init")
		cmd.Dir = t.workDir
		stdoutStderr, err := cmd.CombinedOutput()
		if err != nil {
			t.initErr = fmt.Errorf("%s\n%s", stdoutStderr, err)
		}
	})

	return t.initErr
}

// apply runs "terraform apply" in the project's working directory.
func (t *TestTerraformer) apply() error {
	cmd := exec.Command(t.tfPath, "apply", "-input=false", "-auto-approve")
	cmd.Dir = t.workDir
	stdoutStderr, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("%s\n%s", stdoutStderr, err)
	}

	return nil
}

// destroy runs "terraform destroy" in the project's working directory.
func (t *TestTerraformer) destroy() error {
	cmd := exec.Command(t.tfPath, "destroy", "-input=false", "-auto-approve")
	cmd.Dir = t.workDir
	stdoutStderr, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("%s\n%s", stdoutStderr, err)
	}

	return nil
}

// plan runs "terraform plan" in the project's working directory.
//
// Note that plan is not run as part of the apply workflow; rather,
// it's run to get the data for for importing the state via
// terraform-json. The apply method ignores the plan generated here.
func (t *TestTerraformer) plan() error {
	cmd := exec.Command(t.tfPath, "plan", "-input=false", "-out=plan.tfplan")
	cmd.Dir = t.workDir
	stdoutStderr, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("%s\n%s", stdoutStderr, err)
	}

	return nil
}

// showJson runs "terraform show -json". The output is returned along
// with any error.
//
// Output is only the results of stdout and should be suitable for
// parsing.
//
// This method expects the plan.tfplan file to be generated in the
// working directory already. This can be done with the plan method.
func (t *TestTerraformer) showJson() ([]byte, error) {
	cmd := exec.Command(t.tfPath, "show", "-json", "plan.tfplan")
	cmd.Dir = t.workDir
	output, err := cmd.Output()
	if err != nil {
		exitErr, ok := err.(*exec.ExitError)
		if !ok {
			return nil, err
		}

		return nil, fmt.Errorf("%s\n%s", exitErr.Stderr, exitErr)
	}

	return output, nil
}