Fix filenames of two function spec tests

The tests weren't being run.  Total tests increase from 2742 to 2769.

Also fix 'when using a class extending String' test.
It had been failing with...
```
RuntimeError:
       can't modify frozen AlsoString
```

1 files changed, 9 insertions, 0 deletions

diff --git a/spec/functions/is_function_available_spec.rb b/spec/functions/is_function_available_spec.rb
new file mode 100755
index 0000000..44f08c0
--- /dev/null
+++ b/spec/functions/is_function_available_spec.rb
@@ -0,0 +1,9 @@
+require 'spec_helper'
+
+describe 'is_function_available' 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 { is_expected.to run.with_params('one', 'two').and_raise_error(Puppet::ParseError, /wrong number of arguments/i) }
+  it { is_expected.to run.with_params('include').and_return(true) }
+  it { is_expected.to run.with_params('no_such_function').and_return(false) }
+end