[BACKPORT] add simulated state serialization between tofu test runs (#2274) (#2276)

Signed-off-by: ollevche <ollevche@gmail.com>

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## 1.8.8 (unreleased)
 
+BUG FIXES:
+* `tofu test` now removes outputs of destroyed modules between different test runs. ([#2274](https://github.com/opentofu/opentofu/pull/2274))
 
 
 ## 1.8.7

internal/command/test.go

@@ -6,6 +6,7 @@
 package command
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"log"
@@ -28,6 +29,7 @@ import (
 	"github.com/opentofu/opentofu/internal/moduletest"
 	"github.com/opentofu/opentofu/internal/plans"
 	"github.com/opentofu/opentofu/internal/states"
+	"github.com/opentofu/opentofu/internal/states/statefile"
 	"github.com/opentofu/opentofu/internal/tfdiags"
 	"github.com/opentofu/opentofu/internal/tofu"
 )
@@ -455,6 +457,26 @@ func (runner *TestFileRunner) ExecuteTestFile(file *moduletest.File) {
 
 		state, updatedState := runner.ExecuteTestRun(run, file, runner.States[key].State, config)
 		if updatedState {
+			var err error
+
+			// We need to simulate state serialization between multiple runs
+			// due to its side effects. One of such side effects is removal
+			// of destroyed non-root module outputs. This is not handled
+			// during graph walk since those values are not stored in the
+			// state file. This is more of a weird workaround instead of a
+			// proper fix, unfortunately.
+			state, err = simulateStateSerialization(state)
+			if err != nil {
+				run.Diagnostics = run.Diagnostics.Append(&hcl.Diagnostic{
+					Severity: hcl.DiagError,
+					Summary:  "Failure during state serialization",
+					Detail:   err.Error(),
+				})
+
+				// We cannot reuse state later so that's a hard stop.
+				return
+			}
+
 			// Only update the most recent run and state if the state was
 			// actually updated by this change. We want to use the run that
 			// most recently updated the tracked state as the cleanup
@@ -1261,3 +1283,24 @@ func (runner *TestFileRunner) prepareInputVariablesForAssertions(config *configs
 		config.Module.Variables = currentVars
 	}, diags
 }
+
+// simulateStateSerialization takes a state, serializes it, deserializes it
+// and then returns. This is useful for state writing side effects without
+// actually writing a state file.
+func simulateStateSerialization(state *states.State) (*states.State, error) {
+	buff := &bytes.Buffer{}
+
+	f := statefile.New(state, "", 0)
+
+	err := statefile.Write(f, buff, encryption.StateEncryptionDisabled())
+	if err != nil {
+		return nil, fmt.Errorf("writing state to buffer: %w", err)
+	}
+
+	f, err = statefile.Read(buff, encryption.StateEncryptionDisabled())
+	if err != nil {
+		return nil, fmt.Errorf("reading state from buffer: %w", err)
+	}
+
+	return f.State, nil
+}

internal/command/test_test.go

@@ -820,6 +820,10 @@ func TestTest_Modules(t *testing.T) {
 			expected: "main.tftest.hcl... pass\n  run \"setup\"... pass\n  run \"test\"... pass\n\nSuccess! 2 passed, 0 failed.\n",
 			code:     0,
 		},
+		"destroyed_mod_outputs": {
+			expected: "main.tftest.hcl... pass\n  run \"first_apply\"... pass\n  run \"second_apply\"... pass\n\nSuccess! 2 passed, 0 failed.\n",
+			code:     0,
+		},
 	}
 
 	for name, tc := range tcs {

internal/command/testdata/test/destroyed_mod_outputs/main.tf

@@ -0,0 +1,9 @@
+variable "numbers" {
+    type = set(string)
+}
+
+module "mod" {
+    source = "./mod"
+    for_each = var.numbers
+    val = each.key
+}

internal/command/testdata/test/destroyed_mod_outputs/main.tftest.hcl

@@ -0,0 +1,21 @@
+run "first_apply" {
+  variables {
+    numbers = [ "a", "b" ]
+  }
+
+  assert {
+    condition     = length(module.mod) == 2
+    error_message = "Amount of module outputs is wrong"
+  }
+}
+
+run "second_apply" {
+  variables {
+    numbers = [ "c", "d" ]
+  }
+
+  assert {
+    condition     = length(module.mod) == 2
+    error_message = "Amount of module outputs is wrong (persisted outputs?)"
+  }
+}

internal/command/testdata/test/destroyed_mod_outputs/mod/main.tf

@@ -0,0 +1,11 @@
+variable "val" {
+}
+
+output "val" {
+    value = "${var.val}_${test_resource.resource.id}"
+}
+
+resource "test_resource" "resource" {
+  id = "598318e0"
+  value = var.val
+}