fix(windows): on Windows, throw useful error when package contains no…

… binaries(#142)

Fixes: #137 

* fixed(index): on Windows, throw useful error when package contains no binaries

* test(index): test that on Windows,  a useful error message is returned when there are no binaries

index.js

@@ -86,6 +86,9 @@ function npx (argv) {
               if (process.platform === 'win32') {
                 bins = bins.filter(b => b !== 'etc' && b !== 'node_modules')
               }
+              if (bins.length < 1) {
+                throw new Error(Y()`command not found: ${argv.command}`)
+              }
               const cmd = new RegExp(`^${argv.command}(?:\\.cmd)?$`, 'i')
               const matching = bins.find(b => b.match(cmd))
               return path.resolve(results.bin, bins[matching] || bins[0])

test/index.js

@@ -281,3 +281,16 @@ test('noisy npx with --quiet arg on windows', {
     t.end()
   })
 })
+
+test('nice error message when no binaries on windows', {
+  skip: !isWindows && 'Only on Windows is the error message inscrutable'
+}, t => {
+  return child.spawn('node', [
+    NPX_ESC, '0'
+  ], {stdio: 'pipe'}).then(res => {
+    throw new Error('Should not have succeeded')
+  }, err => {
+    t.equal(err.stderr.split('\n')[1].trim(), 'command not found: 0')
+    t.end()
+  })
+})