test: increase readline coverage

PR-URL: nodejs#12761
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/test-readline.js

@@ -0,0 +1,45 @@
+'use strict';
+const common = require('../common');
+const { PassThrough } = require('stream');
+const readline = require('readline');
+const assert = require('assert');
+
+{
+  const input = new PassThrough();
+  const rl = readline.createInterface({
+    terminal: true,
+    input: input
+  });
+
+  rl.on('line', common.mustCall((data) => {
+    assert.strictEqual(data, 'abc');
+  }));
+
+  input.end('abc');
+}
+
+{
+  const input = new PassThrough();
+  const rl = readline.createInterface({
+    terminal: true,
+    input: input
+  });
+
+  rl.on('line', common.mustNotCall('must not be called before newline'));
+
+  input.write('abc');
+}
+
+{
+  const input = new PassThrough();
+  const rl = readline.createInterface({
+    terminal: true,
+    input: input
+  });
+
+  rl.on('line', common.mustCall((data) => {
+    assert.strictEqual(data, 'abc');
+  }));
+
+  input.write('abc\n');
+}