diff --git a/mmv1/third_party/terraform/tests/data_source_google_billing_account_test.go b/mmv1/third_party/terraform/tests/data_source_google_billing_account_test.go
index d57598ed7d8f..e12b00314e28 100644
--- a/mmv1/third_party/terraform/tests/data_source_google_billing_account_test.go
+++ b/mmv1/third_party/terraform/tests/data_source_google_billing_account_test.go
@@ -9,7 +9,7 @@ import (
 )
 
 func TestAccDataSourceGoogleBillingAccount_byFullName(t *testing.T) {
-	billingId := getTestBillingAccountFromEnv(t)
+	billingId := getTestMasterBillingAccountFromEnv(t)
 	name := "billingAccounts/" + billingId
 
 	vcrTest(t, resource.TestCase{
@@ -29,7 +29,7 @@ func TestAccDataSourceGoogleBillingAccount_byFullName(t *testing.T) {
 }
 
 func TestAccDataSourceGoogleBillingAccount_byShortName(t *testing.T) {
-	billingId := getTestBillingAccountFromEnv(t)
+	billingId := getTestMasterBillingAccountFromEnv(t)
 	name := "billingAccounts/" + billingId
 
 	vcrTest(t, resource.TestCase{
@@ -49,7 +49,7 @@ func TestAccDataSourceGoogleBillingAccount_byShortName(t *testing.T) {
 }
 
 func TestAccDataSourceGoogleBillingAccount_byFullNameClosed(t *testing.T) {
-	billingId := getTestBillingAccountFromEnv(t)
+	billingId := getTestMasterBillingAccountFromEnv(t)
 	name := "billingAccounts/" + billingId
 
 	vcrTest(t, resource.TestCase{
diff --git a/mmv1/third_party/terraform/tests/resource_google_project_test.go b/mmv1/third_party/terraform/tests/resource_google_project_test.go
index 44506121468b..ed7c5ae8fce3 100644
--- a/mmv1/third_party/terraform/tests/resource_google_project_test.go
+++ b/mmv1/third_party/terraform/tests/resource_google_project_test.go
@@ -123,6 +123,8 @@ func TestAccProject_create(t *testing.T) {
 func TestAccProject_billing(t *testing.T) {
 	t.Parallel()
 	org := getTestOrgFromEnv(t)
+	// This is a second billing account that can be charged, which is used only in this test to
+	// verify that a project can update its billing account.
 	skipIfEnvNotSet(t, "GOOGLE_BILLING_ACCOUNT_2")
 	billingId2 := os.Getenv("GOOGLE_BILLING_ACCOUNT_2")
 	billingId := getTestBillingAccountFromEnv(t)
diff --git a/mmv1/third_party/terraform/tests/resource_logging_bucket_config_test.go b/mmv1/third_party/terraform/tests/resource_logging_bucket_config_test.go
index fda3da4063b8..560fdda43d13 100644
--- a/mmv1/third_party/terraform/tests/resource_logging_bucket_config_test.go
+++ b/mmv1/third_party/terraform/tests/resource_logging_bucket_config_test.go
@@ -131,7 +131,7 @@ func TestAccLoggingBucketConfigBillingAccount_basic(t *testing.T) {
 
 	context := map[string]interface{}{
 		"random_suffix":        randString(t, 10),
-		"billing_account_name": "billingAccounts/" + getTestBillingAccountFromEnv(t),
+		"billing_account_name": "billingAccounts/" + getTestMasterBillingAccountFromEnv(t),
 		"org_id":               getTestOrgFromEnv(t),
 	}
 
diff --git a/mmv1/third_party/terraform/utils/provider_test.go.erb b/mmv1/third_party/terraform/utils/provider_test.go.erb
index 8d2c771de7ee..8611068fc7ef 100644
--- a/mmv1/third_party/terraform/utils/provider_test.go.erb
+++ b/mmv1/third_party/terraform/utils/provider_test.go.erb
@@ -104,6 +104,8 @@ var orgTargetEnvVars = []string{
 	"GOOGLE_ORG_2",
 }
 
+// This is the billing account that will be charged for the infrastructure used during testing. For
+// that reason, it is also the billing account used for creating new projects.
 var billingAccountEnvVars = []string{
 	"GOOGLE_BILLING_ACCOUNT",
 }
@@ -118,6 +120,8 @@ type VcrSource struct {
 
 var sources map[string]VcrSource
 
+// This is the billing account that will be modified to test billing-related functionality. It is
+// expected to have more permissions granted to the test user and support subaccounts.
 var masterBillingAccountEnvVars = []string{
 	"GOOGLE_MASTER_BILLING_ACCOUNT",
 }
@@ -838,11 +842,15 @@ func getTestOrgTargetFromEnv(t *testing.T) string {
 	return MultiEnvSearch(orgTargetEnvVars)
 }
 
+// This is the billing account that will be charged for the infrastructure used during testing. For
+// that reason, it is also the billing account used for creating new projects.
 func getTestBillingAccountFromEnv(t *testing.T) string {
 	skipIfEnvNotSet(t, billingAccountEnvVars...)
 	return MultiEnvSearch(billingAccountEnvVars)
 }
 
+// This is the billing account that will be modified to test billing-related functionality. It is
+// expected to have more permissions granted to the test user and support subaccounts.
 func getTestMasterBillingAccountFromEnv(t *testing.T) string {
 	skipIfEnvNotSet(t, masterBillingAccountEnvVars...)
 	return MultiEnvSearch(masterBillingAccountEnvVars)