Modifying ExpectKnown<Value|OutputValue|OutputValueAtPath> to allow f…

…or checking of null values (#266)

knownvalue/null.go

@@ -0,0 +1,34 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package knownvalue
+
+import (
+	"fmt"
+)
+
+var _ Check = NullValue{}
+
+// NullValue is a Check for asserting equality between the value supplied
+// to NullValueExact and the value passed to the CheckValue method.
+type NullValue struct{}
+
+// CheckValue determines whether the passed value is of nil.
+func (v NullValue) CheckValue(other any) error {
+	if other != nil {
+		return fmt.Errorf("expected value nil for NullValue check, got: %T", other)
+	}
+
+	return nil
+}
+
+// String returns the string representation of nil.
+func (v NullValue) String() string {
+	return "nil"
+}
+
+// NullValueExact returns a Check for asserting equality nil
+// and the value passed to the CheckValue method.
+func NullValueExact() NullValue {
+	return NullValue{}
+}

knownvalue/null_test.go

@@ -0,0 +1,61 @@
+// Copyright (c) HashiCorp, Inc.
+// SPDX-License-Identifier: MPL-2.0
+
+package knownvalue_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+
+	"github.com/hashicorp/terraform-plugin-testing/knownvalue"
+)
+
+func TestNullValue_CheckValue(t *testing.T) {
+	t.Parallel()
+
+	testCases := map[string]struct {
+		self          knownvalue.NullValue
+		other         any
+		expectedError error
+	}{
+		"zero-nil": {},
+		"zero-other": {
+			other: nil, // checking against the underlying value field zero-value
+		},
+		"not-nil": {
+			self:          knownvalue.NullValueExact(),
+			other:         false,
+			expectedError: fmt.Errorf("expected value nil for NullValue check, got: bool"),
+		},
+		"equal": {
+			self:  knownvalue.NullValueExact(),
+			other: nil,
+		},
+	}
+
+	for name, testCase := range testCases {
+		name, testCase := name, testCase
+
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			got := testCase.self.CheckValue(testCase.other)
+
+			if diff := cmp.Diff(got, testCase.expectedError, equateErrorMessage); diff != "" {
+				t.Errorf("unexpected difference: %s", diff)
+			}
+		})
+	}
+}
+
+func TestNullValue_String(t *testing.T) {
+	t.Parallel()
+
+	got := knownvalue.NullValueExact().String()
+
+	if diff := cmp.Diff(got, "nil"); diff != "" {
+		t.Errorf("unexpected difference: %s", diff)
+	}
+}

statecheck/expect_known_output_value.go

@@ -6,7 +6,6 @@ package statecheck
 import (
 	"context"
 	"fmt"
-	"reflect"
 
 	tfjson "github.com/hashicorp/terraform-json"
 
@@ -56,27 +55,8 @@ func (e expectKnownOutputValue) CheckState(ctx context.Context, req CheckStateRe
 		return
 	}
 
-	if result == nil {
-		resp.Error = fmt.Errorf("value is null")
-
-		return
-	}
-
-	switch reflect.TypeOf(result).Kind() {
-	case reflect.Bool,
-		reflect.Map,
-		reflect.Slice,
-		reflect.String:
-		if err := e.knownValue.CheckValue(result); err != nil {
-			resp.Error = err
-
-			return
-		}
-	default:
-		errorStr := fmt.Sprintf("unrecognised output type: %T, known value type is %T", result, e.knownValue)
-		errorStr += "\n\nThis is an error in statecheck.ExpectKnownOutputValue.\nPlease report this to the maintainers."
-
-		resp.Error = fmt.Errorf(errorStr)
+	if err := e.knownValue.CheckValue(result); err != nil {
+		resp.Error = err
 
 		return
 	}

statecheck/expect_known_output_value_at_path.go

@@ -6,7 +6,6 @@ package statecheck
 import (
 	"context"
 	"fmt"
-	"reflect"
 
 	tfjson "github.com/hashicorp/terraform-json"
 
@@ -57,27 +56,8 @@ func (e expectKnownOutputValueAtPath) CheckState(ctx context.Context, req CheckS
 		return
 	}
 
-	if result == nil {
-		resp.Error = fmt.Errorf("value is null")
-
-		return
-	}
-
-	switch reflect.TypeOf(result).Kind() {
-	case reflect.Bool,
-		reflect.Map,
-		reflect.Slice,
-		reflect.String:
-		if err := e.knownValue.CheckValue(result); err != nil {
-			resp.Error = err
-
-			return
-		}
-	default:
-		errorStr := fmt.Sprintf("unrecognised output type: %T, known value type is %T", result, e.knownValue)
-		errorStr += "\n\nThis is an error in statecheck.ExpectKnownOutputValueAtPath.\nPlease report this to the maintainers."
-
-		resp.Error = fmt.Errorf(errorStr)
+	if err := e.knownValue.CheckValue(result); err != nil {
+		resp.Error = err
 
 		return
 	}