diff --git a/lib/puppet/parser/functions/fqdn_rand_string.rb b/lib/puppet/parser/functions/fqdn_rand_string.rb
index 69041b2..e9636c2 100644
--- a/lib/puppet/parser/functions/fqdn_rand_string.rb
+++ b/lib/puppet/parser/functions/fqdn_rand_string.rb
@@ -1,45 +1,45 @@
 # frozen_string_literal: true
 
 Puppet::Parser::Functions.newfunction(
   :fqdn_rand_string,
   arity: -2,
   type: :rvalue,
   doc: <<-DOC,
   @summary
     Generates a random alphanumeric string. Combining the `$fqdn` fact and an
     optional seed for repeatable randomness.
 
   Optionally, you can specify a character set for the function (defaults to alphanumeric).
 
   Arguments
   * An integer, specifying the length of the resulting string.
   * Optionally, a string specifying the character set.
   * Optionally, a string specifying the seed for repeatable randomness.
 
   @return [String]
 
   @example Example Usage:
     fqdn_rand_string(10)
     fqdn_rand_string(10, 'ABCDEF!@$%^')
     fqdn_rand_string(10, '', 'custom seed')
   DOC
 ) do |args|
   raise(ArgumentError, 'fqdn_rand_string(): wrong number of arguments (0 for 1)') if args.empty?
   Puppet::Parser::Functions.function('is_integer')
   raise(ArgumentError, 'fqdn_rand_string(): first argument must be a positive integer') unless function_is_integer([args[0]]) && args[0].to_i > 0
   raise(ArgumentError, 'fqdn_rand_string(): second argument must be undef or a string') unless args[1].nil? || args[1].is_a?(String)
 
   Puppet::Parser::Functions.function('fqdn_rand')
 
   length = args.shift.to_i
   charset = args.shift.to_s.chars.to_a
 
   charset = (0..9).map { |i| i.to_s } + ('A'..'Z').to_a + ('a'..'z').to_a if charset.empty?
 
   rand_string = ''
   for current in 1..length # rubocop:disable Style/For : An each loop would not work correctly in this circumstance
-    rand_string << charset[function_fqdn_rand([charset.size, (args + [current.to_s]).join(':')]).to_i]
+    rand_string += charset[function_fqdn_rand([charset.size, (args + [current.to_s]).join(':')]).to_i]
   end
 
   rand_string
 end
diff --git a/spec/functions/validate_x509_rsa_key_pair_spec.rb b/spec/functions/validate_x509_rsa_key_pair_spec.rb
index 81e6c73..08a2423 100644
--- a/spec/functions/validate_x509_rsa_key_pair_spec.rb
+++ b/spec/functions/validate_x509_rsa_key_pair_spec.rb
@@ -1,182 +1,181 @@
 # frozen_string_literal: true
 
 require 'spec_helper'
 
 describe 'validate_x509_rsa_key_pair' do
   let(:valid_cert) do
     <<DOC
 -----BEGIN CERTIFICATE-----
 MIIC9jCCAeCgAwIBAgIRAK11n3X7aypJ7FPM8UFyAeowCwYJKoZIhvcNAQELMBIx
 EDAOBgNVBAoTB0FjbWUgQ28wHhcNMTUxMTIzMjIzOTU4WhcNMTYxMTIyMjIzOTU4
 WjASMRAwDgYDVQQKEwdBY21lIENvMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIB
 CgKCAQEAz9bY/piKahD10AiJSfbI2A8NG5UwRz0r9T/WfvNVdhgrsGFgNQjvpUoZ
 nNJpQIHBbgMOiXqfATFjJl5FjEkSf7GUHohlGVls9MX2JmVvknzsiitd75H/EJd+
 N+k915lix8Vqmj8d1CTlbF/8tEjzANI67Vqw5QTuqebO7rkIUvRg6yiRfSo75FK1
 RinCJyl++kmleBwQZBInQyg95GvJ5JTqMzBs67DeeyzskDhTeTePRYVF2NwL8QzY
 htvLIBERTNsyU5i7nkxY5ptUwgFUwd93LH4Q19tPqL5C5RZqXxhE51thOOwafm+a
 W/cRkqYqV+tv+j1jJ3WICyF1JNW0BQIDAQABo0swSTAOBgNVHQ8BAf8EBAMCAKAw
 EwYDVR0lBAwwCgYIKwYBBQUHAwEwDAYDVR0TAQH/BAIwADAUBgNVHREEDTALggls
 b2NhbGhvc3QwCwYJKoZIhvcNAQELA4IBAQAzRo0hpVTrFQZLIXpwvKwZVGvJdCkV
 P95DTsSk/VTGV+/YtxrRqks++hJZnctm2PbnTsCAoIP3AMx+vicCKiKrxvpsLU8/
 +6cowUbcuGMdSQktwDqbAgEhQlLsETll06w1D/KC+ejOc4+LRn3GQcEyGDtMk/EX
 IeAvBZHr4/kVXWnfo6kzCLcku1f8yE/yDEFClZe9XV1Lk/s+3YfXVtNnMJJ1giZI
 QVOe6CkmuQq+4AtIeW8aLkvlfp632jag1F77a1y+L268koKkj0hBMrtcErVQaxmq
 xym0+soR4Tk4pTIGckeFglrLxkP2JpM/yTwSEAVlmG9vgTliYKyR0uMl
 -----END CERTIFICATE-----
 DOC
   end
 
   let(:valid_key) do
     <<DOC
 -----BEGIN RSA PRIVATE KEY-----
 MIIEogIBAAKCAQEAz9bY/piKahD10AiJSfbI2A8NG5UwRz0r9T/WfvNVdhgrsGFg
 NQjvpUoZnNJpQIHBbgMOiXqfATFjJl5FjEkSf7GUHohlGVls9MX2JmVvknzsiitd
 75H/EJd+N+k915lix8Vqmj8d1CTlbF/8tEjzANI67Vqw5QTuqebO7rkIUvRg6yiR
 fSo75FK1RinCJyl++kmleBwQZBInQyg95GvJ5JTqMzBs67DeeyzskDhTeTePRYVF
 2NwL8QzYhtvLIBERTNsyU5i7nkxY5ptUwgFUwd93LH4Q19tPqL5C5RZqXxhE51th
 OOwafm+aW/cRkqYqV+tv+j1jJ3WICyF1JNW0BQIDAQABAoIBADAiZ/r+xP+vkd5u
 O61/lCBFzBlZQecdybJw6HJaVK6XBndA9hESUr4LHUdui6W+51ddKd65IV4bXAUk
 zCKjQb+FFvLDT/bA+TTvLATUdTSN7hJJ3OWBAHuNOlQklof6JCB0Hi4+89+P8/pX
 eKUgR/cmuTMDT/iaXdPHeqFbBQyA1ZpQFRjN5LyyJMS/9FkywuNc5wlpsArtc51T
 gIKENUZCuPhosR+kMFc2iuTNvqZWPhvouSrmhi2O6nSqV+oy0+irlqSpCF2GsCI8
 72TtLpq94Grrq0BEH5avouV+Lp4k83vO65OKCQKUFQlxz3Xkxm2U3J7KzxqnRtM3
 /b+cJ/kCgYEA6/yOnaEYhH/7ijhZbPn8RujXZ5VGJXKJqIuaPiHMmHVS5p1j6Bah
 2PcnqJA2IlLs3UloN+ziAxAIH6KCBiwlQ/uPBNMMaJsIjPNBEy8axjndKhKUpidg
 R0OJ7RQqMShOJ8akrSfWdPtXC/GBuwCYE//t77GgZaIMO3FcT9EKA48CgYEA4Xcx
 Fia0Jg9iyAhNmUOXI6hWcGENavMx01+x7XFhbnMjIKTZevFfTnTkrX6HyLXyGtMU
 gHOn+k4PE/purI4ARrKO8m5wYEKqSIt4dBMTkIXXirfQjXgfjR8E4T/aPe5fOFZo
 7OYuxLRtzmG1C2sW4txwKAKX1LaWcVx/RLSttSsCgYBbcj8Brk+F6OJcqYFdzXGJ
 OOlf5mSMVlopyg83THmwCqbZXtw8L6kAHqZrl5airmfDSJLuOQlMDoZXW+3u3mSC
 d5TwVahVUN57YDgzaumBLyMZDqIz0MZqVy23hTzkV64Rk9R0lR9xrYQJyMhw4sYL
 2f0mCTsSpzz+O+t9so+i2QKBgEC38gMlwPhb2kMI/x1LZYr6uzUu5qcYf+jowy4h
 KZKGwkKQj0zXFEB1FV8nvtpCP+irRmtIx6L13SYi8LnfWPzyLE4ynVdES5TfVAgd
 obQOdzx+XwL8xDHCAaiWp5K3ZeXKB/xYZnxYPlzLdyh76Ond1OPnOqX4c16+6llS
 c7pZAoGATd9NckT0XtXLEsF3IraDivq8dP6bccX2DNfS8UeEvRRrRwpFpSRrmuGb
 jbG4yzoIX4RjQfj/z48hwhJB+cKiN9WwcPsFXtHe7v3F6BRwK0JUfrCiXad8/SGZ
 KAf7Dfqi608zBdnPWHacre2Y35gPHB00nFQOLS6u46aBNSq07YA=
 -----END RSA PRIVATE KEY-----
 DOC
   end
 
   let(:another_valid_key) do
     <<DOC
 -----BEGIN RSA PRIVATE KEY-----
 MIIEpAIBAAKCAQEAoISxYJBTPAeAzFnm+lE/ljLlmGal2Xr3vwZKkvJiuKA/m4QJ
 0ZNdtkBSDOVuG2dXVv6W4sChRtsCdvuVe7bjTYvlU8TWM3VEJDL9l9cRXScxxlKQ
 Xwb35y1yV35NJfaK/jzm9KcErtQQs1RxvGlWRaohmLM8uQcuhjZfMsSlQoHQD5LX
 sbPtk82RPyxYc1dj2vsaoi1VvuP2+jv4xLQOmNJY1bT5GTurqiltmxEtWhNNmGg0
 2wtK00ifqLVO5HNc3gXQCDM2M99Sbmn1YtbrgsU9xMYfcPmvQvb+YoKskyoqck+c
 HR//hi7vslbxABrny15LBkEfRc4TickphSGYXwIDAQABAoIBAATEzGw8/WwMIQRx
 K06GeWgh7PZBHm4+m/ud2TtSXiJ0CE+7dXs3cJJIiOd/LW08/bhE6gCkjmYHfaRB
 Ryicv1X/cPmzIFX5BuQ4a5ZGOmrVDkKBE27vSxAgJoR46RvWnjx9XLMp/xaekDxz
 psldK8X4DvV1ZbltgDFWji947hvyqUtHdKnkQnc5j7aCIFJf9GMfzaeeDPMaL8WF
 mVL4iy9EAOjNOHBshZj/OHyU5FbJ8ROwZQlCOiLCdFegftSIXt8EYDnjB3BdsALH
 N6hquqrD7xDKyRbTD0K7lqxUubuMwTQpi61jZD8TBTXEPyFVAnoMpXkc0Y+np40A
 YiIsR+kCgYEAyrc4Bh6fb9gt49IXGXOSRZ5i5+TmJho4kzIONrJ7Ndclwx9wzHfh
 eGBodWaw5CxxQGMf4vEiaZrpAiSFeDffBLR+Wa2TFE5aWkdYkR34maDjO00m4PE1
 S+YsZoGw7rGmmj+KS4qv2T26FEHtUI+F31RC1FPohLsQ22Jbn1ORipsCgYEAyrYB
 J2Ncf2DlX1C0GfxyUHQOTNl0V5gpGvpbZ0WmWksumYz2kSGOAJkxuDKd9mKVlAcz
 czmN+OOetuHTNqds2JJKKJy6hJbgCdd9aho3dId5Xs4oh4YwuFQiG8R/bJZfTlXo
 99Qr02L7MmDWYLmrR3BA/93UPeorHPtjqSaYU40CgYEAtmGfWwokIglaSDVVqQVs
 3YwBqmcrla5TpkMLvLRZ2/fktqfL4Xod9iKu+Klajv9ZKTfFkXWno2HHL7FSD/Yc
 hWwqnV5oDIXuDnlQOse/SeERb+IbD5iUfePpoJQgbrCQlwiB0TNGwOojR2SFMczf
 Ai4aLlQLx5dSND9K9Y7HS+8CgYEAixlHQ2r4LuQjoTs0ytwi6TgqE+vn3K+qDTwc
 eoods7oBWRaUn1RCKAD3UClToZ1WfMRQNtIYrOAsqdveXpOWqioAP0wE5TTOuZIo
 GiWxRgIsc7TNtOmNBv+chCdbNP0emxdyjJUIGb7DFnfCw47EjHnn8Guc13uXaATN
 B2ZXgoUCgYAGa13P0ggUf5BMJpBd8S08jKRyvZb1CDXcUCuGtk2yEx45ern9U5WY
 zJ13E5z9MKKO8nkGBqrRfjJa8Xhxk4HKNFuzHEet5lvNE7IKCF4YQRb0ZBhnb/78
 +4ZKjFki1RrWRNSw9TdvrK6qaDKgTtCTtfRVXAYQXUgq7lSFOTtL3A==
 -----END RSA PRIVATE KEY-----
 DOC
   end
   # rubocop:enable Layout/IndentHeredoc
 
   let(:valid_cert_but_indented) do
     valid_cert.gsub(%r{^}, '  ')
   end
 
   let(:valid_key_but_indented) do
     valid_key.gsub(%r{^}, '  ')
   end
 
   let(:malformed_cert) do
     truncate_middle(valid_cert)
   end
 
   let(:malformed_key) do
     truncate_middle(valid_key)
   end
 
   let(:bad_cert) do
     'foo'
   end
 
   let(:bad_key) do
     'bar'
   end
 
   context 'with function signature validation' do
     it { is_expected.not_to eq(nil) }
     it { is_expected.to run.with_params.and_raise_error(Puppet::ParseError, %r{wrong number of arguments}i) }
     it { is_expected.to run.with_params(0, 1, 2, 3).and_raise_error(Puppet::ParseError, %r{wrong number of arguments}i) }
   end
 
   context 'with valid input' do
     describe 'valid certificate and key' do
       it { is_expected.to run.with_params(valid_cert, valid_key) }
     end
   end
 
   context 'with bad input' do
     describe 'valid certificate, valid but indented key' do
       it { is_expected.to run.with_params(valid_cert, valid_key_but_indented).and_raise_error(Puppet::ParseError, %r{Not a valid RSA key}) }
     end
 
     describe 'valid certificate, malformed key' do
       it { is_expected.to run.with_params(valid_cert, malformed_key).and_raise_error(Puppet::ParseError, %r{Not a valid RSA key}) }
     end
 
     describe 'valid certificate, bad key' do
       it { is_expected.to run.with_params(valid_cert, bad_key).and_raise_error(Puppet::ParseError, %r{Not a valid RSA key}) }
     end
 
     describe 'valid but indented certificate, valid key' do
       it { is_expected.to run.with_params(valid_cert_but_indented, valid_key).and_raise_error(Puppet::ParseError, %r{Not a valid x509 certificate}) }
     end
 
     describe 'malformed certificate, valid key' do
       it { is_expected.to run.with_params(malformed_cert, valid_key).and_raise_error(Puppet::ParseError, %r{Not a valid x509 certificate}) }
     end
 
     describe 'bad certificate, valid key' do
       it { is_expected.to run.with_params(bad_cert, valid_key).and_raise_error(Puppet::ParseError, %r{Not a valid x509 certificate}) }
     end
 
     describe 'validate certificate and key; certficate not signed by key' do
       it { is_expected.to run.with_params(valid_cert, another_valid_key).and_raise_error(Puppet::ParseError, %r{Certificate signature does not match supplied key}) }
     end
 
     describe 'valid cert and key but arguments in wrong order' do
       it { is_expected.to run.with_params(valid_key, valid_cert).and_raise_error(Puppet::ParseError, %r{Not a valid x509 certificate}) }
     end
 
     describe 'non-string arguments' do
       it { is_expected.to run.with_params({}, {}).and_raise_error(Puppet::ParseError, %r{is not a string}) }
       it { is_expected.to run.with_params(1, 1).and_raise_error(Puppet::ParseError, %r{is not a string}) }
       it { is_expected.to run.with_params(true, true).and_raise_error(Puppet::ParseError, %r{is not a string}) }
       it { is_expected.to run.with_params('foo', {}).and_raise_error(Puppet::ParseError, %r{is not a string}) }
       it { is_expected.to run.with_params(1, 'bar').and_raise_error(Puppet::ParseError, %r{is not a string}) }
       it { is_expected.to run.with_params('baz', true).and_raise_error(Puppet::ParseError, %r{is not a string}) }
     end
   end
 
   def truncate_middle(string)
     chars_to_truncate = 48
     middle = (string.length / 2).floor
     start_pos = middle - (chars_to_truncate / 2)
     end_pos = middle + (chars_to_truncate / 2)
 
-    string[start_pos...end_pos] = ''
-    string
+    string[0..start_pos] + string[end_pos..-1]
   end
 end