add test for filters in statically defined collection elements

<tool id="collection_creates_pair_filter" name="collection_creates_pair_filter" version="0.1.0">

  <description>test if filters in statically defined collection elements work</description>

  <command>

    for i in A B C D; do

      echo "\$i" > "\$i".txt;

    done

  </command>

  <inputs>

    <param name="decide" type="boolean"/>

  </inputs>

  <outputs>

    <collection name="paired_output" format="txt" type="list" label="Split Pair">

      <data name="A" from_work_dir="A.txt">

        <filter>decide</filter>

      </data>

      <data name="B" from_work_dir="B.txt">

        <filter>decide</filter>

      </data>

      <data name="C" from_work_dir="C.txt">

        <filter>not decide</filter>

      </data>

      <data name="D" from_work_dir="D.txt">

        <filter>not decide</filter>

      </data>

    </collection>

  </outputs>

  <tests>

    <test expect_num_outputs="3">

      <param name="decide" value="true" />

      <output_collection name="paired_output" type="paired">

        <element name="A" ftype="txt">

          <assert_contents>

            <has_line line="A" />

          </assert_contents>

        </element>

        <element name="B" ftype="txt">

          <assert_contents>

            <has_line line="B" />

          </assert_contents>

        </element>

      </output_collection>

    </test>

    <test expect_num_outputs="3">

      <param name="decide" value="false" />

      <output_collection name="paired_output" type="paired">

        <element name="C" ftype="txt">

          <assert_contents>

            <has_line line="C" />

          </assert_contents>

        </element>

        <element name="D" ftype="txt">

          <assert_contents>

            <has_line line="D" />

          </assert_contents>

        </element>

      </output_collection>

    </test>

  </tests>

</tool>

  <tool file="collection_mixed_param.xml" />

  <tool file="collection_two_paired.xml" />

  <tool file="collection_creates_pair.xml" />

  <tool file="collection_creates_pair_filter.xml" />

  <tool file="collection_creates_pair_format.xml" />

  <tool file="collection_creates_pair_from_type.xml" />

  <tool file="collection_creates_pair_from_work_dir.xml" />