Add tests for robots.txt being fetched and cached

Does not yet include testing that a page URL disallowed by robots
is not queued, as I haven't yet been able to find a Webrecorder-
managed site with a robots.txt with disallows to test against.

tests/robots_txt.test.js

@@ -0,0 +1,35 @@
+import child_process from "child_process";
+
+test("test robots.txt is fetched and cached", async () => {
+  const res = child_process.execSync(
+    "docker run -v $PWD/test-crawls:/crawls webrecorder/browsertrix-crawler crawl --url https://specs.webrecorder.net/ --url https://webrecorder.net/ --scopeType page --robots --logging debug",
+  );
+
+  const log = res.toString();
+
+  // robots.txt not found
+  expect(
+    log.indexOf(
+      '"logLevel":"debug","context":"robots","message":"Fetching robots.txt","details":{"url":"https://specs.webrecorder.net/robots.txt"}}',
+    ) > 0,
+  ).toBe(true);
+
+  expect(
+    log.indexOf(
+      '"logLevel":"debug","context":"robots","message":"Robots.txt not fetched","details":{"url":"https://specs.webrecorder.net/robots.txt","status":404}}',
+    ) > 0,
+  ).toBe(true);
+
+  // robots.txt found and cached
+  expect(
+    log.indexOf(
+      '"logLevel":"debug","context":"robots","message":"Fetching robots.txt","details":{"url":"https://webrecorder.net/robots.txt"}}',
+    ) > 0,
+  ).toBe(true);
+
+  expect(
+    log.indexOf(
+      '"logLevel":"debug","context":"robots","message":"Caching robots.txt body","details":{"url":"https://webrecorder.net/robots.txt"}}',
+    ) > 0,
+  ).toBe(true);
+});