tests/provider: Prepare EC2-Classic handling to remove reseting defau…

…lt region environment variable and better document existing provider initialization

Reference: #8316
Reference: #15737
Reference: #15791

Output from acceptance testing in AWS Commercial (DynamoDB to verify existing testAccProviderFactories handling):

```
--- PASS: TestAccAWSDynamoDbTable_Replica_Single (274.15s)

--- PASS: TestAccAWSRedshiftSecurityGroup_basic (10.87s)
--- PASS: TestAccAWSRedshiftSecurityGroup_ingressCidr (10.88s)
--- PASS: TestAccAWSRedshiftSecurityGroup_ingressSecurityGroup (12.45s)
--- PASS: TestAccAWSRedshiftSecurityGroup_updateIngressCidr (24.07s)
--- PASS: TestAccAWSRedshiftSecurityGroup_updateIngressSecurityGroup (27.14s)
```

Output from acceptance testing in AWS GovCloud (US):

```
--- SKIP: TestAccAWSRedshiftSecurityGroup_updateIngressCidr (2.50s)
--- SKIP: TestAccAWSRedshiftSecurityGroup_basic (2.50s)
--- SKIP: TestAccAWSRedshiftSecurityGroup_ingressCidr (2.50s)
--- SKIP: TestAccAWSRedshiftSecurityGroup_ingressSecurityGroup (2.50s)
--- SKIP: TestAccAWSRedshiftSecurityGroup_updateIngressSecurityGroup (2.50s)
```

aws/ec2_classic_test.go

@@ -0,0 +1,84 @@
+package aws
+
+import (
+	"context"
+	"os"
+	"sync"
+	"testing"
+
+	"github.com/aws/aws-sdk-go/aws/endpoints"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/terraform"
+)
+
+const (
+	// EC2-Classic region testing environment variable name
+	Ec2ClassicRegionEnvVar = "AWS_EC2_CLASSIC_REGION"
+)
+
+// testAccProviderEc2Classic is the EC2-Classic provider instance
+//
+// This Provider can be used in testing code for API calls without requiring
+// the use of saving and referencing specific ProviderFactories instances.
+//
+// testAccEC2ClassicPreCheck(t) must be called before using this provider instance.
+var testAccProviderEc2Classic *schema.Provider
+
+// testAccProviderEc2ClassicConfigure ensures the provider is only configured once
+var testAccProviderEc2ClassicConfigure sync.Once
+
+// testAccEC2ClassicPreCheck verifies AWS credentials and that EC2-Classic is supported
+func testAccEC2ClassicPreCheck(t *testing.T) {
+	// Since we are outside the scope of the Terraform configuration we must
+	// call Configure() to properly initialize the provider configuration.
+	testAccProviderEc2ClassicConfigure.Do(func() {
+		testAccProviderEc2Classic = Provider()
+
+		config := map[string]interface{}{
+			"region": testAccGetEc2ClassicRegion(),
+		}
+
+		err := testAccProviderEc2Classic.Configure(context.Background(), terraform.NewResourceConfigRaw(config))
+
+		if err != nil {
+			t.Fatal(err)
+		}
+	})
+
+	client := testAccProviderEc2Classic.Meta().(*AWSClient)
+	platforms := client.supportedplatforms
+	region := client.region
+	if !hasEc2Classic(platforms) {
+		t.Skipf("this test can only run in EC2-Classic, platforms available in %s: %q", region, platforms)
+	}
+}
+
+// testAccEc2ClassicRegionProviderConfig is the Terraform provider configuration for EC2-Classic region testing
+//
+// Testing EC2-Classic assumes no other provider configurations are necessary
+// and overwrites the "aws" provider configuration.
+func testAccEc2ClassicRegionProviderConfig() string {
+	return testAccRegionalProviderConfig(testAccGetEc2ClassicRegion())
+}
+
+// testAccGetEc2ClassicRegion returns the EC2-Classic region for testing
+func testAccGetEc2ClassicRegion() string {
+	v := os.Getenv(Ec2ClassicRegionEnvVar)
+
+	if v != "" {
+		return v
+	}
+
+	if testAccGetPartition() == endpoints.AwsPartitionID {
+		return endpoints.UsEast1RegionID
+	}
+
+	return testAccGetRegion()
+}
+
+// testAccProviderFactoriesEc2Classic initializes providers for EC2-Classic testing.
+//
+// Deprecated: This will be replaced with testAccProviderFactories when it only returns the "aws" provider
+func testAccProviderFactoriesEc2Classic() map[string]func() (*schema.Provider, error) {
+	return testAccProviderFactoriesInit(nil, []string{ProviderNameAws})
+}

aws/provider_test.go

@@ -24,6 +24,31 @@ import (
 	"github.com/hashicorp/terraform-plugin-sdk/v2/terraform"
 )
 
+const (
+	// Provider name for single configuration testing
+	ProviderNameAws = "aws"
+
+	// Provider name for alternate configuration testing
+	ProviderNameAwsAlternate = "awsalternate"
+
+	// Provider name for alternate account and alternate region configuration testing
+	ProviderNameAwsAlternateAccountAlternateRegion = "awsalternateaccountalternateregion"
+
+	// Provider name for alternate account and same region configuration testing
+	ProviderNameAwsAlternateAccountSameRegion = "awsalternateaccountsameregion"
+
+	// Provider name for same account and alternate region configuration testing
+	ProviderNameAwsSameAccountAlternateRegion = "awssameaccountalternateregion"
+
+	// Provider name for third configuration testing
+	ProviderNameAwsThird = "awsthird"
+
+	// Provider name for hardcoded us-east-1 configuration testing
+	//
+	// Deprecated: This will be replaced with service specific providers
+	ProviderNameAwsUsEast1 = "awsus-east-1"
+)
+
 const rfc3339RegexPattern = `^[0-9]{4}-(0[1-9]|1[012])-(0[1-9]|[12][0-9]|3[01])[Tt]([01][0-9]|2[0-3]):[0-5][0-9]:[0-5][0-9](\.[0-9]+)?([Zz]|([+-]([01][0-9]|2[0-3]):[0-5][0-9]))$`
 const uuidRegexPattern = `[a-f0-9]{8}-[a-f0-9]{4}-[1-5][a-f0-9]{3}-[ab89][a-f0-9]{3}-[a-f0-9]{12}`
 
@@ -34,31 +59,73 @@ var TestAccSkip = func(t *testing.T, message string) {
 	t.Skip(message)
 }
 
+// testAccProviders is a static map of provider types and their associated provider instance.
+//
+// Deprecated: Terraform Plugin SDK version 2 uses TestCase.ProviderFactories
+// but supports this value in TestCase.Providers for backwards compatibility.
+// In the future Providers: testAccProviders will be changed to
+// ProviderFactories: testAccProviderFactories
 var testAccProviders map[string]*schema.Provider
+
+// testAccProviderFactories initializes and returns Provider slice elements of a provider type and function that returns the provider instance
+//
+// Using this function will initialize all listed provider types as gRPC
+// plugins for every test, which is inefficient and can cause ulimit issues.
+//
+// Deprecated: Use specific ProviderFactories functions such as testAccProviderFactoriesEc2Classic instead.
+// In the future this will be changed to return only the aws provider and not accept a parameter.
 var testAccProviderFactories func(providers *[]*schema.Provider) map[string]func() (*schema.Provider, error)
+
+// testAccProvider is the "main" provider instance
+//
+// This Provider can be used in testing code for API calls without requiring
+// the use of saving and referencing specific ProviderFactories instances.
+//
+// testAccPreCheck(t) must be called before using this provider instance.
 var testAccProvider *schema.Provider
+
+// testAccProviderFunc is a function that returns the "main" provider instance
+//
+// Deprecated: Use testAccAwsRegionProviderFunc instead.
+// In the future this will be changed to be compatible with ProviderFactories.
 var testAccProviderFunc func() *schema.Provider
 
 func init() {
 	testAccProvider = Provider()
 	testAccProviders = map[string]*schema.Provider{
-		"aws": testAccProvider,
+		ProviderNameAws: testAccProvider,
 	}
 	testAccProviderFactories = func(providers *[]*schema.Provider) map[string]func() (*schema.Provider, error) {
-		// this is an SDKV2 compatible hack, the "factory" functions are
-		// effectively singletons for the lifecycle of a resource.Test
-		var providerNames = []string{"aws", "awseast", "awswest", "awsalternate", "awsus-east-1", "awsalternateaccountalternateregion", "awsalternateaccountsameregion", "awssameaccountalternateregion", "awsthird"}
-		var factories = make(map[string]func() (*schema.Provider, error), len(providerNames))
-		for _, name := range providerNames {
-			p := Provider()
-			factories[name] = func() (*schema.Provider, error) { //nolint:unparam
-				return p, nil
-			}
+		return testAccProviderFactoriesInit(providers, []string{
+			ProviderNameAws,
+			ProviderNameAwsAlternate,
+			ProviderNameAwsAlternateAccountAlternateRegion,
+			ProviderNameAwsAlternateAccountSameRegion,
+			ProviderNameAwsSameAccountAlternateRegion,
+			ProviderNameAwsThird,
+			ProviderNameAwsUsEast1,
+		})
+	}
+	testAccProviderFunc = func() *schema.Provider { return testAccProvider }
+}
+
+// testAccProviderFactoriesInit creates ProviderFactories for the provider under testing.
+func testAccProviderFactoriesInit(providers *[]*schema.Provider, providerNames []string) map[string]func() (*schema.Provider, error) {
+	var factories = make(map[string]func() (*schema.Provider, error), len(providerNames))
+
+	for _, name := range providerNames {
+		p := Provider()
+
+		factories[name] = func() (*schema.Provider, error) { //nolint:unparam
+			return p, nil
+		}
+
+		if providers != nil {
 			*providers = append(*providers, p)
 		}
-		return factories
 	}
-	testAccProviderFunc = func() *schema.Provider { return testAccProvider }
+
+	return factories
 }
 
 func TestProvider(t *testing.T) {
@@ -519,16 +586,6 @@ func testAccAlternateRegionPreCheck(t *testing.T) {
 	}
 }
 
-func testAccEC2ClassicPreCheck(t *testing.T) {
-	client := testAccProvider.Meta().(*AWSClient)
-	platforms := client.supportedplatforms
-	region := client.region
-	if !hasEc2Classic(platforms) {
-		t.Skipf("This test can only run in EC2 Classic, platforms available in %s: %q",
-			region, platforms)
-	}
-}
-
 func testAccEC2VPCOnlyPreCheck(t *testing.T) {
 	client := testAccProvider.Meta().(*AWSClient)
 	platforms := client.supportedplatforms
@@ -697,31 +754,16 @@ provider "awssameaccountalternateregion" {
 
 // Deprecated: Use testAccMultipleRegionProviderConfig instead
 func testAccAlternateRegionProviderConfig() string {
-	//lintignore:AT004
-	return fmt.Sprintf(`
-provider "awsalternate" {
-  region = %[1]q
-}
-`, testAccGetAlternateRegion())
+	return testAccNamedRegionalProviderConfig(ProviderNameAwsAlternate, testAccGetAlternateRegion())
 }
 
 func testAccMultipleRegionProviderConfig(regions int) string {
 	var config strings.Builder
 
-	//lintignore:AT004
-	fmt.Fprintf(&config, `
-provider "awsalternate" {
-  region = %[1]q
-}
-`, testAccGetAlternateRegion())
+	config.WriteString(testAccNamedRegionalProviderConfig(ProviderNameAwsAlternate, testAccGetAlternateRegion()))
 
 	if regions >= 3 {
-		//lintignore:AT004
-		fmt.Fprintf(&config, `
-provider "awsthird" {
-  region = %[1]q
-}
-`, testAccGetThirdRegion())
+		config.WriteString(testAccNamedRegionalProviderConfig(ProviderNameAwsThird, testAccGetThirdRegion()))
 	}
 
 	return config.String()
@@ -749,19 +791,41 @@ provider "aws" {
 `, key1)
 }
 
+// testAccNamedRegionalProviderConfig creates a new provider named configuration with a region.
+//
+// This can be used to build multiple provider configuration testing.
+func testAccNamedRegionalProviderConfig(providerName string, region string) string {
+	//lintignore:AT004
+	return fmt.Sprintf(`
+provider %[1]q {
+  region = %[2]q
+}
+`, providerName, region)
+}
+
+// testAccRegionalProviderConfig creates a new provider configuration with a region.
+//
+// This can only be used for single provider configuration testing as it
+// overwrites the "aws" provider configuration.
+func testAccRegionalProviderConfig(region string) string {
+	//lintignore:AT004
+	return fmt.Sprintf(`
+provider "aws" {
+  region = %[1]q
+}
+`, region)
+}
+
 // Provider configuration hardcoded for us-east-1.
 // This should only be necessary for testing ACM Certificates with CloudFront
 // related infrastucture such as API Gateway Domain Names for EDGE endpoints,
 // CloudFront Distribution Viewer Certificates, and Cognito User Pool Domains.
 // Other valid usage is for services only available in us-east-1 such as the
 // Cost and Usage Reporting and Pricing services.
+//
+// Deprecated: This will be replaced with service specific provider configurations.
 func testAccUsEast1RegionProviderConfig() string {
-	//lintignore:AT004
-	return `
-provider "awsus-east-1" {
-  region = "us-east-1"
-}
-`
+	return testAccNamedRegionalProviderConfig(ProviderNameAwsUsEast1, endpoints.UsEast1RegionID)
 }
 
 func testAccAwsRegionProviderFunc(region string, providers *[]*schema.Provider) func() *schema.Provider {