Custom Plan Checks

The package plancheck also provides the PlanCheck interface, which can be implemented for a custom plan check.

The plancheck.CheckPlanRequest contains the current plan file, parsed by the terraform-json package.

Here is an example implementation of a plan check that asserts that every resource change is a no-op, aka, an empty plan:

package example_test

import (
    "context"
    "fmt"

    "github.com/hashicorp/terraform-plugin-testing/plancheck"
)

var _ plancheck.PlanCheck = expectEmptyPlan{}

type expectEmptyPlan struct{}

func (e expectEmptyPlan) CheckPlan(ctx context.Context, req plancheck.CheckPlanRequest, resp *plancheck.CheckPlanResponse) {
    var result error

    for _, rc := range req.Plan.ResourceChanges {
        if !rc.Change.Actions.NoOp() {
            result = errors.Join(result, fmt.Errorf("expected empty plan, but %s has planned action(s): %v", rc.Address, rc.Change.Actions))
        }
    }

    resp.Error = result
}

func ExpectEmptyPlan() plancheck.PlanCheck {
    return expectEmptyPlan{}
}

And example usage:

package example_test

import (
    "context"
    "errors"
    "fmt"
    "testing"

    "github.com/hashicorp/terraform-plugin-testing/helper/resource"
    "github.com/hashicorp/terraform-plugin-testing/plancheck"
)

func Test_CustomPlanCheck_ExpectEmptyPlan(t *testing.T) {
    t.Parallel()

    resource.Test(t, resource.TestCase{
        ExternalProviders: map[string]resource.ExternalProvider{
            "random": {
                Source: "registry.terraform.io/hashicorp/random",
            },
        },
        Steps: []resource.TestStep{
            {
                Config: `resource "random_string" "one" {
                    length = 16
                }`,
            },
            {
                Config: `resource "random_string" "one" {
                    length = 16
                }`,
                ConfigPlanChecks: resource.ConfigPlanChecks{
                    PreApply: []plancheck.PlanCheck{
                        ExpectEmptyPlan(),
                    },
                },
            },
        },
    })
}