fix(formatters) fix invalid json when no results found (#2912)

packages/cli/src/commands/__tests__/lint.test.ts

@@ -261,4 +261,24 @@ describe('lint', () => {
 
     expect(process.stderr.write).nthCalledWith(6, `Error #3: ${chalk.red('original exception')}\n`);
   });
+
+  it('does not write informational message to stdout when format is json and no results found', async () => {
+    (lint as jest.Mock).mockReset();
+    (lint as jest.Mock).mockResolvedValueOnce({ results: [], resolvedRuleset: {} });
+    (formatOutput as jest.Mock).mockReturnValueOnce('[]');
+    (writeOutput as jest.Mock).mockResolvedValueOnce(undefined);
+
+    await run(`lint -f json ./__fixtures__/empty-oas2-document.json`);
+    expect(process.stdout.write).not.toHaveBeenCalledWith(expect.stringContaining('No results'));
+  });
+
+  it('writes informational message to stdout when format is stylish and no results found', async () => {
+    (lint as jest.Mock).mockReset();
+    (lint as jest.Mock).mockResolvedValueOnce({ results: [], resolvedRuleset: {} });
+    (formatOutput as jest.Mock).mockReturnValueOnce('');
+    (writeOutput as jest.Mock).mockResolvedValueOnce(undefined);
+
+    await run(`lint -f stylish ./__fixtures__/empty-oas2-document.json`);
+    expect(process.stdout.write).toHaveBeenCalledWith(expect.stringContaining('No results'));
+  });
 });

packages/cli/src/commands/lint.ts

@@ -223,7 +223,7 @@ const lintCommand: CommandModule = {
 
       if (linterResult.results.length > 0) {
         process.exit(severeEnoughToFail(linterResult.results, failSeverity) ? 1 : 0);
-      } else if (config.quiet !== true) {
+      } else if (config.quiet !== true && !format.includes(OutputFormat.JSON)) {
         const isErrorSeverity = getDiagnosticSeverity(failSeverity) === DiagnosticSeverity.Error;
         process.stdout.write(
           `No results with a severity of '${failSeverity}' ${isErrorSeverity ? '' : 'or higher '}found!\n`,