Implementing expect unknown and null output value plan checks

.changes/unreleased/FEATURES-20231122-084316.yaml

@@ -0,0 +1,6 @@
+kind: FEATURES
+body: 'plancheck: Added `ExpectUnknownOutputValue` built-in plan check, which asserts
+  that a given output value at a specified address is unknown'
+time: 2023-11-22T08:43:16.202152Z
+custom:
+  Issue: "220"

.changes/unreleased/FEATURES-20231122-084409.yaml

@@ -0,0 +1,6 @@
+kind: FEATURES
+body: 'plancheck: Added `ExpectUnknownOutputValueAtPath` built-in plan check, which
+  asserts that a given output value at a specified address, and path is unknown'
+time: 2023-11-22T08:44:09.522934Z
+custom:
+  Issue: "220"

.changes/unreleased/FEATURES-20231122-084501.yaml

@@ -0,0 +1,6 @@
+kind: FEATURES
+body: 'plancheck: Added `ExpectNullOutputValue` built-in plan check, which asserts
+  that a given output value at a specified address is null'
+time: 2023-11-22T08:45:01.330523Z
+custom:
+  Issue: "220"

.changes/unreleased/FEATURES-20231122-084552.yaml

@@ -0,0 +1,6 @@
+kind: FEATURES
+body: 'plancheck: Added `ExpectNullOutputValueAtPath` built-in plan check, which asserts
+  that a given output value at a specified address, and path is null'
+time: 2023-11-22T08:45:52.856267Z
+custom:
+  Issue: "220"

plancheck/expect_null_output_value.go

@@ -0,0 +1,71 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package plancheck
+
+import (
+	"context"
+	"fmt"
+
+	tfjson "github.com/hashicorp/terraform-json"
+
+	"github.com/hashicorp/terraform-plugin-testing/tfjsonpath"
+)
+
+var _ PlanCheck = expectNullOutputValue{}
+
+type expectNullOutputValue struct {
+	outputAddress string
+}
+
+// CheckPlan implements the plan check logic.
+func (e expectNullOutputValue) CheckPlan(ctx context.Context, req CheckPlanRequest, resp *CheckPlanResponse) {
+	var change *tfjson.Change
+
+	for address, oc := range req.Plan.OutputChanges {
+		if e.outputAddress == address {
+			change = oc
+
+			break
+		}
+	}
+
+	if change == nil {
+		resp.Error = fmt.Errorf("%s - Output not found in plan OutputChanges", e.outputAddress)
+
+		return
+	}
+
+	var result any
+	var err error
+
+	switch {
+	case change.Actions.Create():
+		result, err = tfjsonpath.Traverse(change.After, tfjsonpath.Path{})
+	default:
+		result, err = tfjsonpath.Traverse(change.Before, tfjsonpath.Path{})
+	}
+
+	if err != nil {
+		resp.Error = err
+
+		return
+	}
+
+	if result != nil {
+		resp.Error = fmt.Errorf("attribute at path is not null")
+
+		return
+	}
+}
+
+// ExpectNullOutputValue returns a plan check that asserts that the specified output has a null value.
+//
+// Due to implementation differences between the terraform-plugin-sdk and the terraform-plugin-framework, representation of null
+// values may differ. For example, terraform-plugin-sdk based providers may have less precise representations of null values, such
+// as marking whole maps as null rather than individual element values.
+func ExpectNullOutputValue(outputAddress string) PlanCheck {
+	return expectNullOutputValue{
+		outputAddress: outputAddress,
+	}
+}

plancheck/expect_null_output_value_at_path.go

@@ -0,0 +1,73 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package plancheck
+
+import (
+	"context"
+	"fmt"
+
+	tfjson "github.com/hashicorp/terraform-json"
+
+	"github.com/hashicorp/terraform-plugin-testing/tfjsonpath"
+)
+
+var _ PlanCheck = expectNullOutputValueAtPath{}
+
+type expectNullOutputValueAtPath struct {
+	outputAddress string
+	valuePath     tfjsonpath.Path
+}
+
+// CheckPlan implements the plan check logic.
+func (e expectNullOutputValueAtPath) CheckPlan(ctx context.Context, req CheckPlanRequest, resp *CheckPlanResponse) {
+	var change *tfjson.Change
+
+	for address, oc := range req.Plan.OutputChanges {
+		if e.outputAddress == address {
+			change = oc
+
+			break
+		}
+	}
+
+	if change == nil {
+		resp.Error = fmt.Errorf("%s - Output not found in plan OutputChanges", e.outputAddress)
+
+		return
+	}
+
+	var result any
+	var err error
+
+	switch {
+	case change.Actions.Create():
+		result, err = tfjsonpath.Traverse(change.After, e.valuePath)
+	default:
+		result, err = tfjsonpath.Traverse(change.Before, e.valuePath)
+	}
+
+	if err != nil {
+		resp.Error = err
+
+		return
+	}
+
+	if result != nil {
+		resp.Error = fmt.Errorf("attribute at path is not null")
+
+		return
+	}
+}
+
+// ExpectNullOutputValueAtPath returns a plan check that asserts that the specified output has a null value.
+//
+// Due to implementation differences between the terraform-plugin-sdk and the terraform-plugin-framework, representation of null
+// values may differ. For example, terraform-plugin-sdk based providers may have less precise representations of null values, such
+// as marking whole maps as null rather than individual element values.
+func ExpectNullOutputValueAtPath(outputAddress string, valuePath tfjsonpath.Path) PlanCheck {
+	return expectNullOutputValueAtPath{
+		outputAddress: outputAddress,
+		valuePath:     valuePath,
+	}
+}