feat(native): add toHaveStyle

packages/native/src/lib/ElementAssertion.ts

@@ -2,7 +2,8 @@ import { Assertion, AssertionError } from "@assertive-ts/core";
 import { get } from "dot-prop-immutable";
 import { ReactTestInstance } from "react-test-renderer";
 
-import { instanceToString, isEmpty } from "./helpers/helpers";
+import { instanceToString, isEmpty, getFlattenedStyle, styleToString } from "./helpers/helpers";
+import { AssertiveStyle } from "./helpers/types";
 
 export class ElementAssertion extends Assertion<ReactTestInstance> {
   public constructor(actual: ReactTestInstance) {
@@ -200,6 +201,47 @@ export class ElementAssertion extends Assertion<ReactTestInstance> {
     });
   }
 
+  /**
+   * Asserts that a component has the specified style(s) applied.
+   *
+   * This method supports both single style objects and arrays of style objects.
+   * It checks if all specified style properties match on the target element.
+   *
+   * @example
+   * ```
+   * expect(element).toHaveStyle({ backgroundColor: "red" });
+   * expect(element).toHaveStyle([{ backgroundColor: "red" }]);
+   * ```
+   *
+   * @param style - A style object to check for.
+   * @returns the assertion instance
+   */
+  public toHaveStyle(style: AssertiveStyle): this {
+    const stylesOnElement: AssertiveStyle = get(this.actual, "props.style", {});
+
+    const flattenedElementStyle = getFlattenedStyle(stylesOnElement);
+    const flattenedStyle = getFlattenedStyle(style);
+
+    const hasStyle = Object.keys(flattenedStyle)
+                           .every(key => flattenedElementStyle[key] === flattenedStyle[key]);
+
+    const error = new AssertionError({
+      actual: this.actual,
+      message: `Expected element ${this.toString()} to have style: \n${styleToString(flattenedStyle)}`,
+    });
+
+    const invertedError = new AssertionError({
+      actual: this.actual,
+      message: `Expected element ${this.toString()} NOT to have style: \n${styleToString(flattenedStyle)}`,
+    });
+
+    return this.execute({
+      assertWhen: hasStyle,
+      error,
+      invertedError,
+    });
+  }
+
   private isElementDisabled(element: ReactTestInstance): boolean {
     const { type } = element;
     const elementType = type.toString();

packages/native/src/lib/helpers/helpers.ts

@@ -1,5 +1,8 @@
+import { StyleSheet } from "react-native";
 import { ReactTestInstance } from "react-test-renderer";
 
+import { AssertiveStyle, StyleObject } from "./types";
+
 /**
  * Checks if a value is empty.
  *
@@ -31,3 +34,13 @@ export function instanceToString(instance: ReactTestInstance | null): string {
 
   return `<${instance.type.toString()} ... />`;
 }
+
+export function getFlattenedStyle(style: AssertiveStyle): StyleObject {
+    const flattenedStyle = StyleSheet.flatten(style);
+    return flattenedStyle ? (flattenedStyle as StyleObject) : {};
+}
+
+export function styleToString(flattenedStyle: StyleObject): string {
+  const styleEntries = Object.entries(flattenedStyle);
+  return styleEntries.map(([key, value]) => `\t- ${key}: ${String(value)};`).join("\n");
+}

packages/native/src/lib/helpers/types.ts

@@ -0,0 +1,19 @@
+import { ImageStyle, StyleProp, TextStyle, ViewStyle } from "react-native";
+
+/**
+ * Type representing a style that can be applied to a React Native component.
+ * It can be a style for text, view, or image components.
+ */
+export type Style = TextStyle | ViewStyle | ImageStyle;
+
+/**
+ * Type for a style prop that can be applied to a React Native component.
+ * It can be a single style or an array of styles.
+ */
+export type AssertiveStyle = StyleProp<Style>;
+
+/**
+ * Type representing a style object when flattened.
+ * It is a record where the keys are strings and the values can be of any type.
+ */
+export type StyleObject = Record<string, unknown>;

packages/native/test/lib/ElementAssertion.test.tsx

@@ -375,4 +375,151 @@ describe("[Unit] ElementAssertion.test.ts", () => {
       });
     });
   });
+
+  describe(".toHaveStyle", () => {
+    context("when the element contains the target style", () => {
+      it("returns the assertion instance", () => {
+      const element = render(
+        <View testID="id" style={{ backgroundColor: "red" }} />,
+      );
+      const test = new ElementAssertion(element.getByTestId("id"));
+
+      expect(test.toHaveStyle({ backgroundColor: "red" })).toBe(test);
+      expect(() => test.not.toHaveStyle({ backgroundColor: "red" }))
+        .toThrowError(AssertionError)
+        .toHaveMessage("Expected element <View ... /> NOT to have style: \n\t- backgroundColor: red;");
+      });
+    });
+
+    context("when the element does NOT contain the target style", () => {
+      it("throws an error", () => {
+        const element = render(
+        <View testID="id" style={{ opacity: 1 }} />,
+        );
+        const test = new ElementAssertion(element.getByTestId("id"));
+
+        expect(test.not.toHaveStyle({ backgroundColor: "red" })).toBeEqual(test);
+        expect(() => test.toHaveStyle({ backgroundColor: "red" }))
+        .toThrowError(AssertionError)
+        .toHaveMessage("Expected element <View ... /> to have style: \n\t- backgroundColor: red;");
+      });
+    });
+
+    context("when the element contains multiple styles and matches all", () => {
+      it("returns the assertion instance", () => {
+      const element = render(
+        <View testID="id" style={{ backgroundColor: "red", opacity: 0.5 }} />,
+      );
+      const test = new ElementAssertion(element.getByTestId("id"));
+
+      expect(test.toHaveStyle({ backgroundColor: "red", opacity: 0.5 })).toBe(test);
+      expect(() => test.not.toHaveStyle({ backgroundColor: "red", opacity: 0.5 }))
+        .toThrowError(AssertionError)
+        .toHaveMessage(
+          "Expected element <View ... /> NOT to have style: \n\t- backgroundColor: red;\n\t- opacity: 0.5;",
+        );
+      });
+    });
+
+    context("when the element contains multiple styles but does not match all", () => {
+      it("throws an error", () => {
+      const element = render(
+        <View testID="id" style={{ backgroundColor: "red", opacity: 1 }} />,
+      );
+      const test = new ElementAssertion(element.getByTestId("id"));
+
+      expect(test.not.toHaveStyle({ backgroundColor: "red", opacity: 0.5 })).toBeEqual(test);
+      expect(() => test.toHaveStyle({ backgroundColor: "red", opacity: 0.5 }))
+        .toThrowError(AssertionError)
+        .toHaveMessage("Expected element <View ... /> to have style: \n\t- backgroundColor: red;\n\t- opacity: 0.5;");
+      });
+    });
+
+    context("when the element has no style prop", () => {
+      it("throws an error", () => {
+      const element = render(
+        <View testID="id" />,
+      );
+      const test = new ElementAssertion(element.getByTestId("id"));
+
+      expect(test.not.toHaveStyle({ backgroundColor: "red" })).toBeEqual(test);
+      expect(() => test.toHaveStyle({ backgroundColor: "red" }))
+        .toThrowError(AssertionError)
+        .toHaveMessage("Expected element <View ... /> to have style: \n\t- backgroundColor: red;");
+      });
+    });
+
+    context("when the element style is an array and contains the target style", () => {
+      it("returns the assertion instance", () => {
+      const element = render(
+        <View testID="id" style={[{ backgroundColor: "red" }, { opacity: 0.5 }]} />,
+      );
+      const test = new ElementAssertion(element.getByTestId("id"));
+
+      expect(test.toHaveStyle({ backgroundColor: "red", opacity: 0.5 })).toBe(test);
+      expect(() => test.not.toHaveStyle({ backgroundColor: "red", opacity: 0.5 }))
+        .toThrowError(AssertionError)
+        .toHaveMessage(
+          "Expected element <View ... /> NOT to have style: \n\t- backgroundColor: red;\n\t- opacity: 0.5;",
+        );
+      });
+    });
+
+    context("when the passed style is an array and contains the target style", () => {
+      it("returns the assertion instance", () => {
+      const element = render(
+        <View testID="id" style={[{ backgroundColor: "red" }, { opacity: 0.5 }]} />,
+      );
+      const test = new ElementAssertion(element.getByTestId("id"));
+      expect(test.toHaveStyle([{ backgroundColor: "red" }, { opacity: 0.5 }])).toBe(test);
+      expect(() => test.not.toHaveStyle([{ backgroundColor: "red" }, { opacity: 0.5 }]))
+        .toThrowError(AssertionError)
+        .toHaveMessage(
+          "Expected element <View ... /> NOT to have style: \n\t- backgroundColor: red;\n\t- opacity: 0.5;",
+        );
+      });
+    });
+
+    context("when the element style is an array and does not contain the target style", () => {
+      it("throws an error", () => {
+      const element = render(
+        <View testID="id" style={[{ backgroundColor: "blue" }, { opacity: 1 }]} />,
+      );
+      const test = new ElementAssertion(element.getByTestId("id"));
+
+      expect(test.not.toHaveStyle({ backgroundColor: "red" })).toBeEqual(test);
+      expect(() => test.toHaveStyle({ backgroundColor: "red" }))
+        .toThrowError(AssertionError)
+        .toHaveMessage("Expected element <View ... /> to have style: \n\t- backgroundColor: red;");
+      });
+    });
+
+    context("when the style value is undefined", () => {
+      it("throws an error", () => {
+      const element = render(
+        <View testID="id" style={{ backgroundColor: undefined }} />,
+      );
+      const test = new ElementAssertion(element.getByTestId("id"));
+
+      expect(test.not.toHaveStyle({ backgroundColor: "red" })).toBeEqual(test);
+      expect(() => test.toHaveStyle({ backgroundColor: "red" }))
+        .toThrowError(AssertionError)
+        .toHaveMessage("Expected element <View ... /> to have style: \n\t- backgroundColor: red;");
+      });
+    });
+
+    context("when the style value is null", () => {
+      it("throws an error", () => {
+      const element = render(
+        <View testID="id" style={null} />,
+      );
+      const test = new ElementAssertion(element.getByTestId("id"));
+
+      expect(test.not.toHaveStyle({ backgroundColor: "red" })).toBeEqual(test);
+      expect(() => test.toHaveStyle({ backgroundColor: "red" }))
+        .toThrowError(AssertionError)
+        .toHaveMessage("Expected element <View ... /> to have style: \n\t- backgroundColor: red;");
+      });
+    });
+  });
 });