test: increase coverage for repl

Refs: https://coverage.nodejs.org/coverage-7abc7e45b2e17730/lib/internal/repl.js.html#L33

PR-URL: #38559
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

test/parallel/test-repl-envvars.js

@@ -7,6 +7,7 @@ const stream = require('stream');
 const REPL = require('internal/repl');
 const assert = require('assert');
 const inspect = require('util').inspect;
+const { REPL_MODE_SLOPPY, REPL_MODE_STRICT } = require('repl');
 
 const tests = [
   {
@@ -33,6 +34,14 @@ const tests = [
     env: { NODE_NO_READLINE: '0' },
     expected: { terminal: true, useColors: true }
   },
+  {
+    env: { NODE_REPL_MODE: 'sloppy' },
+    expected: { terminal: true, useColors: true, replMode: REPL_MODE_SLOPPY }
+  },
+  {
+    env: { NODE_REPL_MODE: 'strict' },
+    expected: { terminal: true, useColors: true, replMode: REPL_MODE_STRICT }
+  },
 ];
 
 function run(test) {
@@ -54,6 +63,8 @@ function run(test) {
                        `Expected ${inspect(expected)} with ${inspect(env)}`);
     assert.strictEqual(repl.useColors, expected.useColors,
                        `Expected ${inspect(expected)} with ${inspect(env)}`);
+    assert.strictEqual(repl.replMode, expected.replMode || REPL_MODE_SLOPPY,
+                       `Expected ${inspect(expected)} with ${inspect(env)}`);
     for (const key of Object.keys(env)) {
       delete process.env[key];
     }