Move toBeEmptyAssertion to the element assertions

Author: kdquistanchala

packages/native/src/lib/ElementAssertion.ts

@@ -2,7 +2,7 @@ import { Assertion, AssertionError } from "@assertive-ts/core";
 import { get } from "dot-prop-immutable";
 import { ReactTestInstance } from "react-test-renderer";
 
-import { instanceToString } from "./helpers/helpers";
+import { instanceToString, isEmpty } from "./helpers/helpers";
 
 export class ElementAssertion extends Assertion<ReactTestInstance> {
   public constructor(actual: ReactTestInstance) {
@@ -66,6 +66,33 @@ export class ElementAssertion extends Assertion<ReactTestInstance> {
     });
   }
 
+  /**
+   * Check if the element is empty.
+   *
+   * @example
+   * ```
+   * expect(element).toBeEmpty();
+   * ```
+   *
+   * @returns the assertion instance
+   */
+  public toBeEmpty(): this {
+    const error = new AssertionError({
+      actual: this.actual,
+      message: `Expected element ${this.toString()} to be empty.`,
+    });
+    const invertedError = new AssertionError({
+      actual: this.actual,
+      message: `Expected element ${this.toString()} NOT to be empty.`,
+    });
+
+    return this.execute({
+      assertWhen: isEmpty(this.actual.children),
+      error,
+      invertedError,
+    });
+  }
+
   private isElementDisabled(element: ReactTestInstance): boolean {
     const { type } = element;
     const elementType = type.toString();

packages/native/src/lib/ToBeEmptyAssertion.ts

@@ -3,6 +3,7 @@ import { render } from "@testing-library/react-native";
 import {
   View,
   TextInput,
+  Text,
 } from "react-native";
 
 import { ElementAssertion } from "../../src/lib/ElementAssertion";
@@ -129,4 +130,34 @@ describe("[Unit] ElementAssertion.test.ts", () => {
       });
     });
   });
+
+  describe(".toBeEmpty", () => {
+    context("when the element is empty", () => {
+      it("returns the assertion instance", () => {
+        const element = render(<View testID="id" />);
+        const test = new ElementAssertion(element.getByTestId("id"));
+
+        expect(test.toBeEmpty()).toBe(test);
+        expect(() => test.not.toBeEmpty())
+          .toThrowError(AssertionError)
+          .toHaveMessage("Expected element <View ... /> NOT to be empty.");
+      });
+    });
+
+    context("when the element is NOT empty", () => {
+      it("throws an error", () => {
+        const element = render(
+          <View testID="id">
+            <Text>{"Not empty"}</Text>
+          </View>,
+        );
+        const test = new ElementAssertion(element.getByTestId("id"));
+
+        expect(test.not.toBeEmpty()).toBeEqual(test);
+        expect(() => test.toBeEmpty())
+          .toThrowError(AssertionError)
+          .toHaveMessage("Expected element <View ... /> to be empty.");
+      });
+    });
+  });
 });