Fix opentf test crash on nil output (#267)

Co-authored-by: Elbaz <eran.elbaz@env0.com>

internal/command/test_test.go

@@ -152,6 +152,10 @@ func TestTest(t *testing.T) {
 			expected: "3 passed, 0 failed.",
 			code:     0,
 		},
+		"null_output": {
+			expected: "1 passed, 0 failed.",
+			code:     0,
+		},
 	}
 	for name, tc := range tcs {
 		t.Run(name, func(t *testing.T) {
@@ -227,6 +231,11 @@ func TestTest_Full_Output(t *testing.T) {
 			expected: "Blocks of type \"check\" are not expected here.",
 			code:     1,
 		},
+		"not_exists_output": {
+			expected: "Error: Reference to undeclared output value",
+			args:     []string{"-no-color"},
+			code:     1,
+		},
 		"refresh_conflicting_config": {
 			expected: "Incompatible plan options",
 			code:     1,

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

@@ -0,0 +1,2 @@
+resource "test_resource" "resource" {
+}

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

@@ -0,0 +1,6 @@
+run "not_exists" {
+  assert {
+    condition = output.something_that_does_not_exist == null
+    error_message = "Should fail for Reference to undeclared output value"
+  }
+}

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

@@ -0,0 +1,3 @@
+output "my_null_output" {
+  value = null
+}

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

@@ -0,0 +1,6 @@
+run "null" {
+  assert {
+    condition = output.my_null_output == null
+    error_message = "Should work"
+  }
+}

internal/opentf/evaluate.go

@@ -975,17 +975,24 @@ func (d *evaluationStateData) GetOutput(addr addrs.OutputValue, rng tfdiags.Sour
 
 	output := d.Evaluator.State.OutputValue(addr.Absolute(d.ModulePath))
 
-	val := output.Value
-	if val == cty.NilVal {
-		// Not evaluated yet?
-		val = cty.DynamicVal
-	}
+	// https://github.com/opentffoundation/opentf/issues/257
+	// If the output is null - it does not serialize as part of the node_output state https://github.com/opentffoundation/opentf/blob/4b623c56ffe9e6c1dc345e54470b71b0f261297a/internal/opentf/node_output.go#L592-L596
+	// In such a case, we should simply return a nil value because OpenTF test crash to evaluate for invalid memory address or nil pointer dereference
+	if output == nil {
+		return cty.NilVal, diags
+	} else {
+		val := output.Value
+		if val == cty.NilVal {
+			// Not evaluated yet?
+			val = cty.DynamicVal
+		}
 
-	if output.Sensitive {
-		val = val.Mark(marks.Sensitive)
-	}
+		if output.Sensitive {
+			val = val.Mark(marks.Sensitive)
+		}
 
-	return val, diags
+		return val, diags
+	}
 }
 
 func (d *evaluationStateData) GetCheckBlock(addr addrs.Check, rng tfdiags.SourceRange) (cty.Value, tfdiags.Diagnostics) {