adjust server implementation to always keep prior state

echoprovider/server.go

@@ -265,8 +265,10 @@ func (e *echoProviderServer) PlanResourceChange(ctx context.Context, req *tfprot
 		}, nil
 	}
 
-	// If we're updating and the provider config data hasn't changed, return prior state to indicate no diff
-	if priorState.Equal(tftypes.NewValue(echoTestSchema.ValueType(), map[string]tftypes.Value{"data": e.providerConfigData})) {
+	// If the echo resource has prior state, don't plan anything new as it's valid for the ephemeral data to change
+	// between operations and we don't want to produce constant diffs. This resource is only for testing data, which a
+	// single plan/apply should suffice.
+	if !priorState.IsNull() {
 		return &tfprotov6.PlanResourceChangeResponse{
 			PlannedState: req.PriorState,
 		}, nil

echoprovider/server_test.go

@@ -49,44 +49,31 @@ func TestEchoProviderServer_primitive(t *testing.T) {
 				provider "echo" {
 					data = 200
 				}
-				resource "echo" "test_one" {}
+				resource "echo" "test_two" {}
 				`,
 				ConfigPlanChecks: resource.ConfigPlanChecks{
 					PreApply: []plancheck.PlanCheck{
-						plancheck.ExpectUnknownValue("echo.test_one", tfjsonpath.New("data")),
+						plancheck.ExpectUnknownValue("echo.test_two", tfjsonpath.New("data")),
 					},
 				},
 				ConfigStateChecks: []statecheck.StateCheck{
-					statecheck.ExpectKnownValue("echo.test_one", tfjsonpath.New("data"), knownvalue.Int64Exact(200)),
+					statecheck.ExpectKnownValue("echo.test_two", tfjsonpath.New("data"), knownvalue.Int64Exact(200)),
 				},
 			},
 			{
 				Config: `
 				provider "echo" {
 					data = true
 				}
-				resource "echo" "test_one" {}
+				resource "echo" "test_three" {}
 				`,
 				ConfigPlanChecks: resource.ConfigPlanChecks{
 					PreApply: []plancheck.PlanCheck{
-						plancheck.ExpectUnknownValue("echo.test_one", tfjsonpath.New("data")),
+						plancheck.ExpectUnknownValue("echo.test_three", tfjsonpath.New("data")),
 					},
 				},
 				ConfigStateChecks: []statecheck.StateCheck{
-					statecheck.ExpectKnownValue("echo.test_one", tfjsonpath.New("data"), knownvalue.Bool(true)),
-				},
-			},
-			{
-				Config: `
-				provider "echo" {
-					data = true
-				}
-				resource "echo" "test_one" {}
-				`,
-				ConfigPlanChecks: resource.ConfigPlanChecks{
-					PreApply: []plancheck.PlanCheck{
-						plancheck.ExpectEmptyPlan(),
-					},
+					statecheck.ExpectKnownValue("echo.test_three", tfjsonpath.New("data"), knownvalue.Bool(true)),
 				},
 			},
 		},
@@ -130,15 +117,15 @@ func TestEchoProviderServer_complex(t *testing.T) {
 				provider "echo" {
 					data = tomap({"key1": "hello", "key2": "world"})
 				}
-				resource "echo" "test_one" {}
+				resource "echo" "test_two" {}
 				`,
 				ConfigPlanChecks: resource.ConfigPlanChecks{
 					PreApply: []plancheck.PlanCheck{
-						plancheck.ExpectUnknownValue("echo.test_one", tfjsonpath.New("data")),
+						plancheck.ExpectUnknownValue("echo.test_two", tfjsonpath.New("data")),
 					},
 				},
 				ConfigStateChecks: []statecheck.StateCheck{
-					statecheck.ExpectKnownValue("echo.test_one", tfjsonpath.New("data"),
+					statecheck.ExpectKnownValue("echo.test_two", tfjsonpath.New("data"),
 						knownvalue.MapExact(map[string]knownvalue.Check{
 							"key1": knownvalue.StringExact("hello"),
 							"key2": knownvalue.StringExact("world"),
@@ -151,7 +138,7 @@ func TestEchoProviderServer_complex(t *testing.T) {
 				provider "echo" {
 					data = tomap({"key1": "hello", "key2": "world"})
 				}
-				resource "echo" "test_one" {}
+				resource "echo" "test_two" {}
 				`,
 				ConfigPlanChecks: resource.ConfigPlanChecks{
 					PreApply: []plancheck.PlanCheck{
@@ -188,19 +175,6 @@ func TestEchoProviderServer_null(t *testing.T) {
 					statecheck.ExpectKnownValue("echo.test_one", tfjsonpath.New("data"), knownvalue.Null()),
 				},
 			},
-			{
-				Config: `
-				provider "echo" {
-					data = null
-				}
-				resource "echo" "test_one" {}
-				`,
-				ConfigPlanChecks: resource.ConfigPlanChecks{
-					PreApply: []plancheck.PlanCheck{
-						plancheck.ExpectEmptyPlan(),
-					},
-				},
-			},
 		},
 	})
 }

website/docs/plugin/testing/acceptance-tests/ephemeral-resources.mdx

@@ -135,7 +135,7 @@ After including both providers, our test step `Config` references the ephemeral
 ```go
 func TestExampleCloudSecret(t *testing.T) {
   resource.UnitTest(t, resource.TestCase{
-    // .. test case setup from previous step
+    // .. test case setup
 
     Steps: []resource.TestStep{
       {
@@ -161,7 +161,7 @@ The `echo.test_krb` managed resource has a single computed `data` attribute, whi
 ```go
 func TestExampleCloudSecret(t *testing.T) {
   resource.UnitTest(t, resource.TestCase{
-    // .. test case setup from previous step
+    // .. test case setup
 
     Steps: []resource.TestStep{
       {
@@ -194,7 +194,7 @@ You can also reference the entire ephemeral resource instance for assertions, ra
 ```go
 func TestExampleCloudSecret(t *testing.T) {
   resource.UnitTest(t, resource.TestCase{
-    // .. test case setup from previous step
+    // .. test case setup
 
     Steps: []resource.TestStep{
       {
@@ -217,3 +217,58 @@ func TestExampleCloudSecret(t *testing.T) {
   })
 }
 ```
+
+### Caveats with `echo` provider
+
+Since data produced by an ephemeral resource is allowed to change between plan/apply operations, the `echo` resource has special handling to allow this data to be used in the `terraform-plugin-testing` Go module without producing confusing error messages:
+
+* During plan, if the `echo` resource is being created, the `data` attribute will always be marked as unknown.
+* During plan, if the `echo` resource already exists and is not being destroyed, prior state will always be fully preserved regardless of changes to the provider configuration. This essentially means an instance of the `echo` resource is immutable.
+* During refresh, the prior state of the `echo` resource is always returned, regardless of changes to the provider configuration.
+
+Due to this special handling, if multiple test steps are required for testing data, provider developers should create new instances of `echo` for each new test step, for example:
+
+```go
+func TestExampleCloudSecret(t *testing.T) {
+  resource.UnitTest(t, resource.TestCase{
+    // .. test case setup
+
+    Steps: []resource.TestStep{
+      {
+        Config: `
+        ephemeral "examplecloud_secret" "krb" {
+          name = "user_one"
+        }
+
+        provider "echo" {
+          data = ephemeral.examplecloud_secret.krb
+        }
+
+        # First test object -> 1
+        resource "echo" "test_krb_one" {}
+        `,
+        ConfigStateChecks: []statecheck.StateCheck{
+          statecheck.ExpectKnownValue("echo.test_krb_one", tfjsonpath.New("data").AtMapKey("name"), knownvalue.StringExact("user_one")),
+        },
+      },
+      {
+        Config: `
+        ephemeral "examplecloud_secret" "krb" {
+          name = "user_two"
+        }
+
+        provider "echo" {
+          data = ephemeral.examplecloud_secret.krb
+        }
+
+        # New test object -> 2
+        resource "echo" "test_krb_two" {}
+        `,
+        ConfigStateChecks: []statecheck.StateCheck{
+          statecheck.ExpectKnownValue("echo.test_krb_two", tfjsonpath.New("data").AtMapKey("name"), knownvalue.StringExact("user_two")),
+        },
+      },
+    },
+  })
+}
+```