Fixed tofu test when module has no resource (#1409)

Signed-off-by: siddharthasonker95 <158144589+siddharthasonker95@users.noreply.github.com>

CHANGELOG.md

@@ -9,6 +9,7 @@ ENHANCEMENTS:
 
 BUG FIXES:
 * Added a check in the `tofu test` to validate that the names of test run blocks do not contain spaces. ([#1489](https://github.com/opentofu/opentofu/pull/1489))
+* `tofu test` now supports accessing module outputs when the module has no resources. ([#1409](https://github.com/opentofu/opentofu/pull/1409))
 
 ## Previous Releases
 

internal/command/test_test.go

@@ -799,6 +799,10 @@ func TestTest_Modules(t *testing.T) {
 		code     int
 		skip     bool
 	}{
+		"pass_module_with_no_resource": {
+			expected: "main.tftest.hcl... pass\n  run \"run\"... pass\n\nSuccess! 1 passed, 0 failed.\n",
+			code:     0,
+		},
 		"with_nested_setup_modules": {
 			expected: "main.tftest.hcl... pass\n  run \"load_module\"... pass\n\nSuccess! 1 passed, 0 failed.\n",
 			code:     0,

internal/command/testdata/test/pass_module_with_no_resource/first/main.tf

@@ -0,0 +1,7 @@
+module "second" {
+  source = "../second"
+}
+
+output "id" {
+  value = module.second.id
+}

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

@@ -0,0 +1,5 @@
+module "first" {
+  source = "./first"
+}
+
+resource "test_resource" "resource" {}

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

@@ -0,0 +1,8 @@
+run "run" {
+  command = apply
+
+  assert {
+    condition     = module.first.id != 0
+    error_message = "Fail"
+  }
+}

internal/command/testdata/test/pass_module_with_no_resource/second/main.tf

@@ -0,0 +1,5 @@
+resource "test_resource" "resource" {}
+
+output "id" {
+  value = test_resource.resource.id
+}

internal/tofu/test_context.go

@@ -67,6 +67,13 @@ func (ctx *TestContext) EvaluateAgainstPlan(run *moduletest.Run) {
 }
 
 func (ctx *TestContext) evaluate(state *states.SyncState, changes *plans.ChangesSync, run *moduletest.Run, operation walkOperation) {
+	// The state does not include the module that has no resources, making its outputs unusable.
+	// synchronizeStates function synchronizes the state with the planned state, ensuring inclusion of all modules.
+	if ctx.Plan != nil && ctx.Plan.PlannedState != nil &&
+		len(ctx.State.Modules) != len(ctx.Plan.PlannedState.Modules) {
+		state = synchronizeStates(ctx.State, ctx.Plan.PlannedState)
+	}
+
 	data := &evaluationStateData{
 		Evaluator: &Evaluator{
 			Operation: operation,
@@ -186,3 +193,17 @@ func (ctx *TestContext) evaluate(state *states.SyncState, changes *plans.Changes
 		}
 	}
 }
+
+// synchronizeStates compares the planned state to the current state and incorporates any missing modules
+// from the planned state into the current state.
+//
+// If a module has no resources, it is included in the current state to ensure that its output variables are usable.
+func synchronizeStates(state, plannedState *states.State) *states.SyncState {
+	newState := state.DeepCopy()
+	for key, value := range plannedState.Modules {
+		if _, exists := newState.Modules[key]; !exists {
+			newState.Modules[key] = value
+		}
+	}
+	return newState.SyncWrapper()
+}