feat(dom): DOM - toHaveStyle

packages/dom/package.json

@@ -35,6 +35,7 @@
     "test": "NODE_ENV=test mocha"
   },
   "dependencies": {
+    "@adobe/css-tools": "^4.4.3",
     "fast-deep-equal": "^3.1.3",
     "tslib": "^2.6.2"
   },

packages/dom/src/lib/ElementAssertion.ts

@@ -1,4 +1,7 @@
 import { Assertion, AssertionError } from "@assertive-ts/core";
+import equal from "fast-deep-equal";
+
+import { getReceivedStyle, normalizeStyles } from "./helpers/helpers";
 
 export class ElementAssertion<T extends Element> extends Assertion<T> {
 
@@ -142,9 +145,50 @@ export class ElementAssertion<T extends Element> extends Assertion<T> {
     );
   }
 
-  private getClassList(): string[] {
-    return this.actual.className.split(/\s+/).filter(Boolean);
-  }
+  /**
+   * Asserts that the element has the specified CSS styles.
+   *
+   * @example
+   * ```
+   * expect(component).toHaveStyle({ color: 'green', display: 'block' });
+   * ```
+   *
+   * @param expected the expected CSS styles.
+   * @returns the assertion instance.
+   */
+
+  public toHaveStyle(expected: Partial<CSSStyleDeclaration>): this {
+    if (!this.actual.ownerDocument.defaultView) {
+      throw new Error("The element is not attached to a document with a default view.");
+    }
+    if (!(this.actual instanceof HTMLElement)) {
+      throw new Error("The element is not an HTMLElement.");
+    }
+
+    const window = this.actual.ownerDocument.defaultView;
+
+    const received = window.getComputedStyle(this.actual);
+
+    const { props, expectedStyle } = normalizeStyles(expected);
+
+    const receivedStyle = getReceivedStyle(props, received);
+
+    const error = new AssertionError({
+      actual: this.actual,
+      expected: expectedStyle,
+      message: `Expected the element to match the following style:\n${JSON.stringify(expectedStyle, null, 2)}`,
+    });
+    const invertedError = new AssertionError({
+      actual: this.actual,
+      message: `Expected the element to NOT match the following style:\n${JSON.stringify(expectedStyle, null, 2)}`,
+    });
+
+    return this.execute({
+      assertWhen: equal(expectedStyle, receivedStyle),
+      error,
+      invertedError,
+    });
+    }
 
   /**
    * Helper method to assert the presence or absence of class names.
@@ -181,4 +225,8 @@ export class ElementAssertion<T extends Element> extends Assertion<T> {
       invertedError,
     });
   }
+
+  private getClassList(): string[] {
+    return this.actual.className.split(/\s+/).filter(Boolean);
+  }
 }

packages/dom/src/lib/helpers/helpers.ts

@@ -0,0 +1,56 @@
+export interface CssAtRuleAST {
+  declarations: StyleDeclaration[];
+  rules: Rule[];
+}
+
+interface Rule {
+  declarations: StyleDeclaration[];
+  selectors: string[];
+}
+
+interface StyleDeclaration extends Record<string, string> {
+  property: string;
+  value: string;
+}
+
+export const normalizeStyles = (css: Partial<CSSStyleDeclaration>):
+{ expectedStyle: StyleDeclaration; props: string[]; } => {
+  const normalizer = document.createElement("div");
+  document.body.appendChild(normalizer);
+
+  const { props, expectedStyle } = Object.entries(css).reduce(
+    (acc, [property, value]) => {
+
+      if (typeof value !== "string") {
+        return acc;
+      }
+
+      normalizer.style.setProperty(property, value);
+
+      const normalizedValue = window
+        .getComputedStyle(normalizer)
+        .getPropertyValue(property)
+        .trim();
+
+      return {
+        expectedStyle: {
+          ...acc.expectedStyle,
+          [property]: normalizedValue,
+        },
+        props: [...acc.props, property],
+      };
+    },
+    { expectedStyle: {} as StyleDeclaration, props: [] as string[] },
+  );
+
+  document.body.removeChild(normalizer);
+
+  return { expectedStyle, props };
+};
+
+export const getReceivedStyle = (props: string[], received: CSSStyleDeclaration): StyleDeclaration => {
+  return props.reduce((acc, prop) => {
+    acc[prop] = received?.getPropertyValue(prop).trim();
+    return acc;
+  }, {} as StyleDeclaration);
+};

packages/dom/test/unit/lib/ElementAssertion.test.tsx

@@ -257,12 +257,84 @@ describe("[Unit] ElementAssertion.test.ts", () => {
         const test = new ElementAssertion(divTest);
 
         expect(() => test.toHaveAllClasses("foo", "bar", "baz"))
-          .toThrowError(AssertionError)
-          .toHaveMessage('Expected the element to have all of these classes: "foo bar baz"');
+        .toThrowError(AssertionError)
+        .toHaveMessage('Expected the element to have all of these classes: "foo bar baz"');
 
         expect(test.not.toHaveAllClasses("foo", "bar", "baz")).toBeEqual(test);
       });
     });
   });
 
+  describe(".toHaveStyle", () => {
+    context("when the element has the expected style", () => {
+      it("returns the assertion instance", () => {
+        const { getByTestId } = render(
+        <div
+          className="foo bar test"
+          style={{ border: "1px solid black", color: "red", display: "flex" }}
+          data-testid="test-div"
+        />);
+        const divTest = getByTestId("test-div");
+        const test = new ElementAssertion(divTest);
+
+        expect(test.toHaveStyle({ border: "1px solid black", color: "red", display: "flex" })).toBeEqual(test);
+
+        expect(() => test.not.toHaveStyle({ border: "1px solid black", color: "red", display: "flex" }))
+          .toThrowError(AssertionError)
+          .toHaveMessage(
+            // eslint-disable-next-line max-len
+            'Expected the element to NOT match the following style:\n{\n  "border": "1px solid black",\n  "color": "rgb(255, 0, 0)",\n  "display": "flex"\n}',
+          );
+      });
+    });
+
+    context("when the element does not have the expected style", () => {
+        it("throws an assertion error", () => {
+          const { getByTestId } = render(
+            <div
+              className="foo bar test"
+              style={{ color: "blue", display: "block" }}
+              data-testid="test-div"
+            />,
+          );
+
+          const divTest = getByTestId("test-div");
+          const test = new ElementAssertion(divTest);
+
+          expect(() => test.toHaveStyle(({ border: "1px solid black", color: "red", display: "flex" })))
+            .toThrowError(AssertionError)
+            .toHaveMessage(
+            // eslint-disable-next-line max-len
+            'Expected the element to match the following style:\n{\n  "border": "1px solid black",\n  "color": "rgb(255, 0, 0)",\n  "display": "flex"\n}',
+          );
+
+          expect(test.not.toHaveStyle({ border: "1px solid black", color: "red", display: "flex" })).toBeEqual(test);
+
+        });
+    });
+    context("when the element partially match the style", () => {
+        it("throws an assertion error", () => {
+          const { getByTestId } = render(
+            <div
+              className="foo bar test"
+              style={{ border: "1px solid black", color: "blue", display: "block" }}
+              data-testid="test-div"
+            />,
+          );
+
+          const divTest = getByTestId("test-div");
+          const test = new ElementAssertion(divTest);
+
+          expect(() => test.toHaveStyle(({ color: "red", display: "flex" })))
+            .toThrowError(AssertionError)
+            .toHaveMessage(
+            // eslint-disable-next-line max-len
+          'Expected the element to match the following style:\n{\n  "color": "rgb(255, 0, 0)",\n  "display": "flex"\n}',
+          );
+
+          expect(test.not.toHaveStyle({ border: "1px solid black", color: "red", display: "flex" })).toBeEqual(test);
+
+        });
+    });
+  });
 });

yarn.lock

@@ -12,6 +12,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@adobe/css-tools@npm:^4.4.3":
+  version: 4.4.3
+  resolution: "@adobe/css-tools@npm:4.4.3"
+  checksum: 10/701379c514b7a43ca6681705a93cd57ad79565cfef9591122e9499897550cf324a5e5bb1bc51df0e7433cf0e91b962c90f18ac459dcc98b2431daa04aa63cb20
+  languageName: node
+  linkType: hard
+
 "@ampproject/remapping@npm:^2.2.0":
   version: 2.2.1
   resolution: "@ampproject/remapping@npm:2.2.1"
@@ -49,6 +56,7 @@ __metadata:
   version: 0.0.0-use.local
   resolution: "@assertive-ts/dom@workspace:packages/dom"
   dependencies:
+    "@adobe/css-tools": "npm:^4.4.3"
     "@assertive-ts/core": "workspace:^"
     "@testing-library/dom": "npm:^10.1.0"
     "@testing-library/react": "npm:^16.0.0"