feat: allow FIFOs as test files

lib/cli/lookup-files.js

@@ -109,7 +109,7 @@ module.exports = function lookupFiles(
   // Handle file
   try {
     stat = fs.statSync(filepath);
-    if (stat.isFile()) {
+    if (stat.isFile() || stat.isFIFO()) {
       return filepath;
     }
   } catch (err) {

test/integration/fifo.spec.js

@@ -0,0 +1,58 @@
+'use strict';
+
+const assert = require('node:assert/strict');
+const { execSync }  = require("node:child_process");
+const { createReadStream, createWriteStream, mkdtempSync, unlinkSync }  = require("node:fs");
+const { join }  = require("node:path");
+const { tmpdir }  = require("node:os");
+
+const { invokeMocha, toJSONResult } = require("./helpers");
+
+describe("FIFO support", function () {
+  it("should accept a test passed as a FIFO", function (done) {
+    const dir = mkdtempSync(join(tmpdir(), "mocha-test-fifo-"));
+    const fifoPath = join(dir, 'fifo-1');
+    execSync(`mkfifo ${fifoPath}`);
+
+    const writer = createWriteStream(fifoPath);
+    writer.on('ready', () => {
+      writer.write(`
+        describe('suite from FIFO', () => {
+          it('should pass', () => true);
+        });
+      `, (err) => {
+        if(!err) writer.end();
+      });
+    });
+
+    const args = ['--reporter', 'json', fifoPath];
+
+    invokeMocha(
+      args,
+      (err, res) => {
+        if (err) return done(err);
+
+        try {
+          const result = toJSONResult(res);
+          assert.equal(result.code, 0);
+          assert.equal(result.stats.suites,   1);
+          assert.equal(result.stats.tests,    1);
+          assert.equal(result.stats.passes,   1);
+          assert.equal(result.stats.pending,  0);
+          assert.equal(result.stats.failures, 0);
+
+          // Node hangs if FIFO is never unlinked.
+          unlinkSync(fifoPath);
+
+          done();
+        } catch (err) {
+          // Node hangs if FIFO is never read from.
+          createReadStream(fifoPath).close();
+
+          done(err);
+        }
+      },
+      { stdio: "pipe" },
+    );
+  });
+});