test: avoid usage of package.json files in fixtures directory

---
type: pre_commit_static_analysis_report
description: Results of running static analysis checks when committing changes.
report:
  - task: lint_filenames
    status: passed
  - task: lint_editorconfig
    status: passed
  - task: lint_markdown
    status: na
  - task: lint_package_json
    status: passed
  - task: lint_repl_help
    status: na
  - task: lint_javascript_src
    status: na
  - task: lint_javascript_cli
    status: na
  - task: lint_javascript_examples
    status: na
  - task: lint_javascript_tests
    status: passed
  - task: lint_javascript_benchmarks
    status: na
  - task: lint_python
    status: na
  - task: lint_r
    status: na
  - task: lint_c_src
    status: na
  - task: lint_c_examples
    status: na
  - task: lint_c_benchmarks
    status: na
  - task: lint_c_tests_fixtures
    status: na
  - task: lint_shell
    status: na
  - task: lint_typescript_declarations
    status: na
  - task: lint_typescript_tests
    status: na
  - task: lint_license_headers
    status: passed
---

Author: Planeshifter

lib/node_modules/@stdlib/_tools/eslint/rules/namespace-export-all/test/fixtures/assert/is-complex128/package.json renamed to lib/node_modules/@stdlib/_tools/eslint/rules/namespace-export-all/test/fixtures/assert/is-complex128/_package.json

@@ -23,7 +23,9 @@
 var tape = require( 'tape' );
 var proxyquire = require( 'proxyquire' );
 var RuleTester = require( 'eslint' ).RuleTester;
+var exists = require( '@stdlib/fs/exists' ).sync;
 var contains = require( '@stdlib/assert/contains' );
+var replace = require( '@stdlib/string/replace' );
 
 // Mock the rule with clean path resolution for testing:
 var rule = proxyquire( './../lib/main.js', {
@@ -37,6 +39,12 @@ var rule = proxyquire( './../lib/main.js', {
 		}
 		// Default fallback
 		return '@stdlib/mock/' + pkg;
+	},
+	'@stdlib/fs/exists': {
+		'sync': function mockExists( path ) {
+			path = replace( path, 'package.json', '_package.json' );
+			return exists( path );
+		}
 	}
 });