style: align regexp/to-json with namespace conventions

- Added missing `test/test.main.js` (present in 25/27 siblings, 93%),
  mirroring `test/test.js` but requiring `./../lib/main.js` directly so
  that regressions in `lib/index.js` do not mask bugs in the main
  implementation file.

https://claude.ai/code/session_0151TCuqxNJXJZfy4XEWqKhM

Author: claude

lib/node_modules/@stdlib/regexp/to-json/test/test.main.js

@@ -0,0 +1,149 @@
+/**
+* @license Apache-2.0
+*
+* Copyright (c) 2022 The Stdlib Authors.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*    http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+'use strict';
+
+// MODULES //
+
+var vm = require( 'vm' );
+var tape = require( 'tape' );
+var IS_BROWSER = require( '@stdlib/assert/is-browser' );
+var isPlainObject = require( '@stdlib/assert/is-plain-object' );
+var regexp2json = require( './../lib/main.js' );
+
+
+// VARIABLES //
+
+var opts = {
+	'skip': false
+};
+
+
+// TESTS //
+
+tape( 'main export is a function', function test( t ) {
+	t.ok( true, __filename );
+	t.strictEqual( typeof regexp2json, 'function', 'main export is a function' );
+	t.end();
+});
+
+tape( 'if provided anything other than a regular expression, the function throws an error', function test( t ) {
+	var values;
+	var i;
+
+	values = [
+		'5',
+		5,
+		NaN,
+		null,
+		void 0,
+		true,
+		false,
+		[],
+		{},
+		function noop() {}
+	];
+
+	for ( i = 0; i < values.length; i++ ) {
+		t.throws( badValue( values[i] ), Error, 'throws when provided ' + values[i] );
+	}
+	t.end();
+
+	function badValue( value ) {
+		return function badValue() {
+			regexp2json( value );
+		};
+	}
+});
+
+tape( 'the function returns a JSON object', function test( t ) {
+	var json = regexp2json( /beep/ );
+	t.strictEqual( isPlainObject( json ), true, 'returns expected value' );
+	t.end();
+});
+
+tape( 'the returned JSON object includes a `type` field whose value is equal to "RegExp"', function test( t ) {
+	var json = regexp2json( /beep/ );
+	t.strictEqual( json.type, 'RegExp', 'returns expected value' );
+	t.end();
+});
+
+tape( 'the returned JSON object includes a `pattern` field', function test( t ) {
+	var expected;
+	var values;
+	var json;
+	var i;
+
+	values = [
+		/.*/,
+		/ab+c/,
+		/\/.*^1/
+	];
+
+	expected = [
+		'.*',
+		'ab+c',
+		'\\/.*^1'
+	];
+
+	for ( i = 0; i < values.length; i++ ) {
+		json = regexp2json( values[ i ] );
+		t.strictEqual( json.pattern, expected[ i ], 'returns expected value when provided '+values[ i ].toString() );
+	}
+	t.end();
+});
+
+tape( 'the returned JSON object includes a `flags` field', function test( t ) {
+	var expected;
+	var values;
+	var json;
+	var i;
+
+	values = [
+		/.*/g,
+		/ab+c/i,
+		/\/.*^1/gi
+	];
+
+	expected = [
+		'g',
+		'i',
+		'gi'
+	];
+
+	for ( i = 0; i < values.length; i++ ) {
+		json = regexp2json( values[i] );
+		t.strictEqual( json.flags, expected[ i ], 'returns expected value when provided '+values[ i ].toString() );
+	}
+	t.end();
+});
+
+opts.skip = IS_BROWSER;
+tape( 'the function supports serializing a regular expression from a different realm', opts, function test( t ) {
+	var json;
+	var re;
+
+	re = vm.runInNewContext( '/ab+c/g' );
+	json = regexp2json( re );
+
+	t.strictEqual( json.type, 'RegExp', 'returns expected value' );
+	t.strictEqual( json.pattern, 'ab+c', 'returns expected value' );
+	t.strictEqual( json.flags, 'g', 'returns expected value' );
+
+	t.end();
+});