diff --git a/cli.js b/cli.js
index 149a302..6c668a6 100755
--- a/cli.js
+++ b/cli.js
@@ -33,6 +33,10 @@ function start (opts) {
     opts.cloud = { id: opts.cloud }
   }
 
+  if (opts.rejectUnauthorized) {
+    opts.rejectUnauthorized = opts.rejectUnauthorized !== 'false'
+  }
+
   const stream = pinoElasticSearch(opts)
 
   stream.on('unknown', (line, error) => {
@@ -45,47 +49,66 @@ function start (opts) {
     console.error('Elasticsearch server error:', error)
   })
 
-  if (opts.rejectUnauthorized) {
-    opts.rejectUnauthorized = opts.rejectUnauthorized !== 'false'
-  }
   pump(process.stdin, stream)
 }
 
-const flags = minimist(process.argv.slice(2), {
-  alias: {
-    version: 'v',
-    help: 'h',
-    node: 'n',
-    index: 'i',
-    'flush-bytes': 'f',
-    'flush-interval': 't',
-    'trace-level': 'l',
-    username: 'u',
-    password: 'p',
-    'api-key': 'k',
-    cloud: 'c',
-    'read-config': 'r'
-  },
-  default: {
-    node: 'http://localhost:9200'
-  }
-})
-
-const allowedProps = ['node', 'index', 'flush-bytes', 'flush-interval', 'trace-level', 'username', 'password', 'api-key', 'cloud', 'es-version', 'rejectUnauthorized']
+function startCli (flags) {
+  const allowedProps = [
+    'node',
+    'index',
+    'flush-bytes',
+    'flush-interval',
+    'trace-level',
+    'username',
+    'password',
+    'api-key',
+    'cloud',
+    'es-version',
+    'rejectUnauthorized'
+  ]
 
-if (flags['read-config']) {
-  if (flags['read-config'].match(/.*\.json$/) !== null) {
-    const config = JSON.parse(fs.readFileSync(path.join(process.cwd(), flags['read-config']), 'utf-8'))
-    allowedProps.forEach(key => {
-      if (config[key]) { flags[key] = config[key] }
-    })
+  if (flags['read-config']) {
+    if (flags['read-config'].match(/.*\.json$/) !== null) {
+      const config = JSON.parse(fs.readFileSync(path.join(process.cwd(), flags['read-config']), 'utf-8'))
+      allowedProps.forEach(key => {
+        if (config[key] !== undefined) {
+          flags[key] = config[key]
+        }
+      })
+    }
+    if (flags['read-config'].match(/.*\.js$/) !== null) {
+      const config = require(path.join(process.cwd(), flags['read-config']))
+      allowedProps.forEach(key => {
+        if (config[key] !== undefined) {
+          flags[key] = config[key]
+        }
+      })
+    }
   }
 
-  if (flags['read-config'].match(/.*\.js$/) !== null) {
-    const config = require(path.join(process.cwd(), flags['read-config']))
-    allowedProps.forEach(key => {
-      if (config[key]) { flags[key] = config[key] }
-    })
-  }
+  start(flags)
 }
-start(flags)
+
+if (require.main === module) {
+  startCli(minimist(process.argv.slice(2), {
+    alias: {
+      version: 'v',
+      help: 'h',
+      node: 'n',
+      index: 'i',
+      'flush-bytes': 'f',
+      'flush-interval': 't',
+      'trace-level': 'l',
+      username: 'u',
+      password: 'p',
+      'api-key': 'k',
+      cloud: 'c',
+      'read-config': 'r'
+    },
+    default: {
+      node: 'http://localhost:9200'
+    }
+  }))
+}
+
+module.exports = startCli
diff --git a/test/cli.test.js b/test/cli.test.js
new file mode 100644
index 0000000..e0b182e
--- /dev/null
+++ b/test/cli.test.js
@@ -0,0 +1,107 @@
+'use strict'
+const test = require('tap').test
+const proxyquire = require('proxyquire')
+
+test('CLI: arg node should passed to client constructor', async (t) => {
+  const cli = proxyquire('../cli.js', {
+    pump: () => { },
+    './lib.js': (opts) => {
+      t.same(opts, { node: 'https://custom-node-url:9999' })
+      return {
+        on: () => { }
+      }
+    }
+  })
+
+  cli({ node: 'https://custom-node-url:9999' })
+})
+
+test('CLI: arg rejectUnauthorized, if set to \'true\', should passed as true (bool) to client constructor', async (t) => {
+  const cli = proxyquire('../cli.js', {
+    pump: () => { },
+    './lib.js': (opts) => {
+      t.same(opts, {
+        node: 'https://custom-node-url:9999',
+        rejectUnauthorized: true
+      })
+      return {
+        on: () => { }
+      }
+    }
+  })
+
+  cli({
+    node: 'https://custom-node-url:9999',
+    rejectUnauthorized: 'true'
+  })
+})
+
+test('CLI: arg rejectUnauthorized, if set to \'false\', should passed as false (bool) to client constructor', async (t) => {
+  const cli = proxyquire('../cli.js', {
+    pump: () => { },
+    './lib.js': (opts) => {
+      t.same(opts, {
+        node: 'https://custom-node-url:9999',
+        rejectUnauthorized: false
+      })
+      return {
+        on: () => { }
+      }
+    }
+  })
+
+  cli({
+    node: 'https://custom-node-url:9999',
+    rejectUnauthorized: 'false'
+  })
+})
+
+test('CLI: arg rejectUnauthorized, if set to anything instead of true or false, should passed as true (bool) to client constructor', async (t) => {
+  const cli = proxyquire('../cli.js', {
+    pump: () => { },
+    './lib.js': (opts) => {
+      t.same(opts, {
+        node: 'https://custom-node-url:9999',
+        rejectUnauthorized: true
+      })
+      return {
+        on: () => { }
+      }
+    }
+  })
+
+  cli({
+    node: 'https://custom-node-url:9999',
+    rejectUnauthorized: 'anything'
+  })
+})
+
+test('CLI: if arg.read-config is set, should read the config file and passed the value (only allowed values)', async (t) => {
+  const cli = proxyquire('../cli.js', {
+    pump: () => { },
+    './lib.js': (opts) => {
+      t.same(opts, {
+        index: 'custom-index',
+        node: 'https://localhost:9200',
+        rejectUnauthorized: false,
+        auth: {
+          username: 'elastic',
+          password: 'pass'
+        },
+        // some keys are redundant, it is intended as it is.
+        // (see function start() in cli.js)
+        'read-config': 'test/exampleConfig.js',
+        username: 'elastic',
+        password: 'pass'
+      })
+      return {
+        on: () => { }
+      }
+    }
+  })
+
+  cli({
+    node: 'https://custom-node-url:9999',
+    'read-config': 'test/exampleConfig.js'
+  })
+})
diff --git a/test/exampleConfig.js b/test/exampleConfig.js
new file mode 100644
index 0000000..93a77d8
--- /dev/null
+++ b/test/exampleConfig.js
@@ -0,0 +1,7 @@
+module.exports = {
+  index: 'custom-index',
+  node: 'https://localhost:9200',
+  rejectUnauthorized: false,
+  username: 'elastic',
+  password: 'pass'
+}