test.scala

class MySpecification extends XsltSpecification(new File("src/test/resources/stylesheets/test.xsl")) {
    "Simple transformation" >> {
        applying(<paragraph>foo</paragraph>) yields(<p>foo</p>)
    }

    "Set mode and parameters" >> {
        applying(<paragraph>foo</paragraph>)
            .withMode("main")
            .withParameters(tunnel = false)("foo" -> "bar", "baz" -> "quux")
            .yields(<p>bar, quux</p>)
    }

    "Apply a template that returns an atomic value" >> {
        applying(<anyElement/>).withMode("returns-atomic-value").yields(6)
    }

    "Call a function that returns an atomic value" >> {
        callingFunction("local", "increment", 1).returns(2)
    }

    "Call a function that takes an element and returns a document node" >> {
        callingFunction("local", "wrap-into-foo", parameters = element(<bar/>)).returns(<foo><bar/></foo>)
    }

    "Call a function that takes and returns an attribute" >> {
        callingFunction("local", "rename-to-baz", parameters = attribute("foo" -> "bar")).returns(attribute("baz" -> "quux"))
    }

    "Call a function that takes mixed parameters" >> {
        callingFunction("local", "mix", 1, element(<foo/>), "bar").returns(<foo/>, BigInteger.valueOf(1), "bar")
    }

    "Call a named template that returns an atomic value" >> {
        callingTemplate("sum").withParameters(tunnel = false)("a" -> 1, "b" -> 2).returns(3)
    }

    "Apply a template that calls doc()" >> {
        applying(<include href="b.xml"/>, MockFile("b.xml", <foo/>)).yields(<foo/>)
    }

    "<xsl:result-document> creates a file in the transient file system" >> {
        applying(<paragraph>foo</paragraph>).withMode("result-document")
            .yieldsNothing and (Fs.hasFile(fileSystem, "foo.xml") must beTrue)
    }.pendingUntilFixed("https://saxonica.plan.io/issues/2771")
}

test.xsl

<?xml version="1.0" encoding="utf-8"?>

<xsl:stylesheet version="2.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:local="local"
  exclude-result-prefixes="xs">

  <xsl:output method="xml" indent="yes"/>

  <xsl:function name="local:increment" as="xs:integer">
    <xsl:param name="integer" as="xs:integer"/>
    <xsl:sequence select="$integer + 1"/>
  </xsl:function>

  <xsl:function name="local:wrap-into-foo" as="document-node()">
    <xsl:param name="el" as="element()"/>

    <xsl:variable name="returned">
      <xsl:element name="foo">
        <xsl:sequence select="$el"/>
      </xsl:element>
    </xsl:variable>

    <xsl:sequence select="$returned"/>
  </xsl:function>

  <xsl:function name="local:rename-to-baz" as="attribute(baz)">
    <xsl:param name="attr" as="attribute(foo)"/>

    <xsl:variable name="new-attr" as="attribute()">
      <xsl:attribute name="baz">quux</xsl:attribute>
    </xsl:variable>

    <xsl:sequence select="$new-attr"/>
  </xsl:function>

  <xsl:function name="local:mix" as="item()+">
    <xsl:param name="int" as="xs:integer"/>
    <xsl:param name="el" as="element()"/>
    <xsl:param name="str" as="xs:string"/>
    <xsl:sequence select="($el, $int, $str)"/>
  </xsl:function>

  <xsl:template match="paragraph">
    <p>
      <xsl:apply-templates select="@* | node()"/>
    </p>
  </xsl:template>

  <xsl:template match="paragraph" mode="main">
    <xsl:param name="foo"/>
    <xsl:param name="baz"/>

    <p>
      <xsl:value-of select="$foo"/>, <xsl:value-of select="$baz"/>
    </p>
  </xsl:template>

  <xsl:template match="paragraph" mode="result-document">
    <!--
    <xsl:result-document href="foo.xml">
      <p>
        <xsl:apply-templates select="@* | node()"/>
      </p>
    </xsl:result-document>
    -->
  </xsl:template>

  <xsl:template match="*" mode="returns-atomic-value" as="xs:integer">
    <xsl:value-of select="sum((1, 2, 3))"/>
  </xsl:template>

  <xsl:template name="sum" as="xs:integer">
    <xsl:param name="a" as="xs:integer"/>
    <xsl:param name="b" as="xs:integer"/>

    <xsl:value-of select="$a + $b"/>
  </xsl:template>

  <xsl:template match="include">
    <xsl:sequence select="doc(resolve-uri(@href, base-uri()))"/>
  </xsl:template>

  <xsl:template match="@* | node()">
    <xsl:copy>
      <xsl:apply-templates select="@* | node()"/>
    </xsl:copy>
  </xsl:template>

</xsl:stylesheet>