Extra TestCheckFuncs to check attribute's string length

.changelog/893.txt

@@ -0,0 +1,3 @@
+```release-note:enhancement
+helper/resource: Add `TestCheckFunc` helpers to check attribute's value length
+```

helper/resource/testing.go

@@ -1031,6 +1031,36 @@ func testCheckResourceAttrPair(isFirst *terraform.InstanceState, nameFirst strin
 	return nil
 }
 
+// TestRangeLengthResourceAttr is a TestCheckFunc which checks that the length of the value
+// in state for the given name/key is within an expected (closed) range.
+func TestRangeLengthResourceAttr(name, key string, min, max int) TestCheckFunc {
+	return checkIfIndexesIntoTypeSet(key, func(s *terraform.State) error {
+		is, err := primaryInstanceState(s, name)
+		if err != nil {
+			return err
+		}
+
+		valLen := len(is.Attributes[key])
+		if valLen < min || valLen > max {
+			return fmt.Errorf(
+				"%s: Attribute '%s' length is %d, which is not within the expected closed range [%d, %d]",
+				name,
+				key,
+				valLen,
+				min,
+				max)
+		}
+
+		return nil
+	})
+}
+
+// TestMatchLengthResourceAttr is a TestCheckFunc which checks that the length of the value
+// in state for the given name/key matches a specific length.
+func TestMatchLengthResourceAttr(name, key string, length int) TestCheckFunc {
+	return TestRangeLengthResourceAttr(name, key, length, length)
+}
+
 // TestCheckOutput checks an output in the Terraform configuration
 func TestCheckOutput(name, value string) TestCheckFunc {
 	return func(s *terraform.State) error {

helper/resource/testing_test.go

@@ -874,6 +874,87 @@ func TestCheckResourceAttr_empty(t *testing.T) {
 	}
 }
 
+func TestTestRangeLengthResourceAttr(t *testing.T) {
+	resName := "test_resource"
+	resKey := "test_key"
+	resVal := "test_value"
+
+	s := terraform.NewState()
+	s.AddModuleState(&terraform.ModuleState{
+		Path: []string{"root"},
+		Resources: map[string]*terraform.ResourceState{
+			resName: {
+				Primary: &terraform.InstanceState{
+					Attributes: map[string]string{
+						resKey: resVal,
+					},
+				},
+			},
+		},
+	})
+
+	t.Run("in_range", func(t *testing.T) {
+		check := TestRangeLengthResourceAttr(resName, resKey, 2, 20)
+		if err := check(s); err != nil {
+			t.Fatal(err)
+		}
+	})
+	t.Run("out_of_range", func(t *testing.T) {
+		check := TestRangeLengthResourceAttr(resName, resKey, 20, 40)
+		if err := check(s); err == nil {
+			t.Fatal(fmt.Errorf("failed to detect attribute '%s.%s' value '%s' length is out of range",
+				resName,
+				resKey,
+				resVal))
+		}
+	})
+}
+
+func TestTestMatchLengthResourceAttr(t *testing.T) {
+	resName := "test_resource"
+	resKey := "test_key"
+	resVal := "test_value"
+
+	s := terraform.NewState()
+	s.AddModuleState(&terraform.ModuleState{
+		Path: []string{"root"},
+		Resources: map[string]*terraform.ResourceState{
+			resName: {
+				Primary: &terraform.InstanceState{
+					Attributes: map[string]string{
+						resKey: resVal,
+					},
+				},
+			},
+		},
+	})
+
+	t.Run("matches_length", func(t *testing.T) {
+		check := TestMatchLengthResourceAttr(resName, resKey, 10)
+		if err := check(s); err != nil {
+			t.Fatal(err)
+		}
+	})
+	t.Run("too_short", func(t *testing.T) {
+		check := TestMatchLengthResourceAttr(resName, resKey, 11)
+		if err := check(s); err == nil {
+			t.Fatal(fmt.Errorf("failed to detect attribute '%s.%s' value '%s' is too short",
+				resName,
+				resKey,
+				resVal))
+		}
+	})
+	t.Run("too_long", func(t *testing.T) {
+		check := TestMatchLengthResourceAttr(resName, resKey, 2)
+		if err := check(s); err == nil {
+			t.Fatal(fmt.Errorf("failed to detect attribute '%s.%s' value '%s' is too long",
+				resName,
+				resKey,
+				resVal))
+		}
+	})
+}
+
 func TestCheckNoResourceAttr_empty(t *testing.T) {
 	s := terraform.NewState()
 	s.AddModuleState(&terraform.ModuleState{