Add DNS lookup tool and tests

tests/dnsService.test.js

@@ -0,0 +1,65 @@
+// Import Node's built-in test tools.
+const test = require("node:test");
+const assert = require("node:assert/strict");
+
+// Import the DNS service.
+const {
+  lookupDns,
+  resolveRecord,
+  RECORD_TYPES,
+} = require("../src/services/dnsService");
+
+test("supports the expected DNS record types", () => {
+  assert.deepEqual(
+    RECORD_TYPES,
+    ["A", "AAAA", "CNAME", "MX", "TXT", "NS"]
+  );
+});
+
+test("resolves A records for example.com", async () => {
+  const records = await resolveRecord("example.com", "A");
+
+  assert.equal(Array.isArray(records), true);
+  assert.equal(records.length > 0, true);
+});
+
+test("returns an array for a missing optional record type", async () => {
+  const records = await resolveRecord(
+    "example.com",
+    "CNAME"
+  );
+
+  assert.equal(Array.isArray(records), true);
+});
+
+test("joins TXT record fragments into strings", async () => {
+  const records = await resolveRecord("google.com", "TXT");
+
+  assert.equal(Array.isArray(records), true);
+
+  records.forEach((record) => {
+    assert.equal(typeof record, "string");
+  });
+});
+
+test("returns all supported record groups", async () => {
+  const result = await lookupDns("example.com");
+
+  assert.equal(result.hostname, "example.com");
+  assert.equal(typeof result.checkedAt, "string");
+  assert.equal(typeof result.records, "object");
+
+  RECORD_TYPES.forEach((recordType) => {
+    assert.equal(
+      Array.isArray(result.records[recordType]),
+      true
+    );
+  });
+});
+
+test("returns a valid ISO timestamp", async () => {
+  const result = await lookupDns("example.com");
+  const timestamp = Date.parse(result.checkedAt);
+
+  assert.equal(Number.isNaN(timestamp), false);
+});