Convert tests to use plain rspec-puppet

Tests in the new style produces the following documentation output:

abs
  should not eq nil
  should run abs() and raise an Puppet::ParseError
  should run abs(-34) and return 34
  should run abs("-34") and return 34
  should run abs(34) and return 34
  should run abs("34") and return 34

1 files changed, 22 insertions, 28 deletions

diff --git a/spec/functions/is_string_spec.rb b/spec/functions/is_string_spec.rb
index 6a0801a..8e459cc 100755
--- a/spec/functions/is_string_spec.rb
+++ b/spec/functions/is_string_spec.rb
@@ -1,34 +1,28 @@
-#! /usr/bin/env ruby -S rspec
 require 'spec_helper'
 
-describe "the is_string function" do
-  let(:scope) { PuppetlabsSpec::PuppetInternals.scope }
+describe 'is_string' do
+  it { is_expected.not_to eq(nil) }
+  it { is_expected.to run.with_params().and_raise_error(Puppet::ParseError, /wrong number of arguments/i) }
+  it {
+    pending("Current implementation ignores parameters after the first.")
+    is_expected.to run.with_params('', '').and_raise_error(Puppet::ParseError, /wrong number of arguments/i)
+  }
 
-  it "should exist" do
-    expect(Puppet::Parser::Functions.function("is_string")).to eq("function_is_string")
-  end
+  it { is_expected.to run.with_params(3).and_return(false) }
+  it { is_expected.to run.with_params('3').and_return(false) }
+  it { is_expected.to run.with_params(-3).and_return(false) }
+  it { is_expected.to run.with_params('-3').and_return(false) }
 
-  it "should raise a ParseError if there is less than 1 arguments" do
-    expect { scope.function_is_string([]) }.to( raise_error(Puppet::ParseError))
-  end
+  it { is_expected.to run.with_params(3.7).and_return(false) }
+  it { is_expected.to run.with_params('3.7').and_return(false) }
+  it { is_expected.to run.with_params(-3.7).and_return(false) }
+  it { is_expected.to run.with_params('3.7').and_return(false) }
 
-  it "should return true if a string" do
-    result = scope.function_is_string(["asdf"])
-    expect(result).to(eq(true))
-  end
-
-  it "should return false if an integer" do
-    result = scope.function_is_string(["3"])
-    expect(result).to(eq(false))
-  end
-
-  it "should return false if a float" do
-    result = scope.function_is_string(["3.23"])
-    expect(result).to(eq(false))
-  end
-
-  it "should return false if an array" do
-    result = scope.function_is_string([["a","b","c"]])
-    expect(result).to(eq(false))
-  end
+  it { is_expected.to run.with_params([]).and_return(false) }
+  it { is_expected.to run.with_params([1]).and_return(false) }
+  it { is_expected.to run.with_params({}).and_return(false) }
+  it { is_expected.to run.with_params(true).and_return(false) }
+  it { is_expected.to run.with_params(false).and_return(false) }
+  it { is_expected.to run.with_params('one').and_return(true) }
+  it { is_expected.to run.with_params('0001234').and_return(true) }
 end