doing some more filecheck tests (#3251)

testing/tests/filecheck.test.js

@@ -22,4 +22,27 @@ describe("checking files", () => {
       "<path> contains an unsafe attribute: 'onload'"
     );
   });
+
+  it("should spot files that are not mentioned in source", async () => {
+    const filePath = path.join(SAMPLES_DIRECTORY, "orphan.png");
+    // Sanity check the test itself
+    console.assert(fs.existsSync(filePath), `${filePath} does not exist`);
+    await expect(checkFile(filePath)).rejects.toThrow("is not mentioned in");
+  });
+
+  it("should spot files that are completely empty", async () => {
+    const filePath = path.join(SAMPLES_DIRECTORY, "zero.gif");
+    // Sanity check the test itself
+    console.assert(fs.existsSync(filePath), `${filePath} does not exist`);
+    await expect(checkFile(filePath)).rejects.toThrow("is 0 bytes");
+  });
+
+  it("should spot mismatch between file-type and file extension", async () => {
+    const filePath = path.join(SAMPLES_DIRECTORY, "png.jpeg");
+    // Sanity check the test itself
+    console.assert(fs.existsSync(filePath), `${filePath} does not exist`);
+    await expect(checkFile(filePath)).rejects.toThrow(
+      "is type 'image/png' but named extension is '.jpeg'"
+    );
+  });
 });