Add image parsing tests

packages/alfa-css/test/value/image/image.spec.ts

@@ -0,0 +1,74 @@
+import { test } from "@siteimprove/alfa-test";
+
+import { Image, Lexer } from "../../../src";
+
+function parse(input: string) {
+  return Image.parse(Lexer.lex(input)).getUnsafe()[1].toJSON();
+}
+
+test("parse() parses an image with relative URL", (t) => {
+  t.deepEqual(parse("url('foo.jpg')"), {
+    type: "image",
+    image: { type: "url", url: "foo.jpg" },
+  });
+});
+
+test("parse() parses an image with absolute URL", (t) => {
+  t.deepEqual(parse("url('https://example.com/foo.jpg')"), {
+    type: "image",
+    image: { type: "url", url: "https://example.com/foo.jpg" },
+  });
+});
+
+test("parse() parses a linear gradient", (t) => {
+  t.deepEqual(parse("linear-gradient(red, blue)"), {
+    type: "image",
+    image: {
+      type: "gradient",
+      kind: "linear",
+      direction: { type: "side", side: "bottom" },
+      items: [
+        {
+          type: "stop",
+          color: { type: "color", format: "named", color: "red" },
+          position: null,
+        },
+        {
+          type: "stop",
+          color: { type: "color", format: "named", color: "blue" },
+          position: null,
+        },
+      ],
+      repeats: false,
+    },
+  });
+});
+
+test("parse() parses a radial gradient", (t) => {
+  t.deepEqual(parse("radial-gradient(red, blue)"), {
+    type: "image",
+    image: {
+      type: "gradient",
+      kind: "radial",
+      shape: { type: "extent", shape: "circle", size: "farthest-corner" },
+      position: {
+        type: "position",
+        horizontal: { type: "keyword", value: "center" },
+        vertical: { type: "keyword", value: "center" },
+      },
+      items: [
+        {
+          type: "stop",
+          color: { type: "color", format: "named", color: "red" },
+          position: null,
+        },
+        {
+          type: "stop",
+          color: { type: "color", format: "named", color: "blue" },
+          position: null,
+        },
+      ],
+      repeats: false,
+    },
+  });
+});