Reference

A precise technical reference, not a tutorial. For a task-oriented introduction see the user guide.

Configuration

Set under the :junit-xml key in project.clj. Unknown keys are rejected rather than ignored.

Key	Type	Default	Description
:output-dir	string	"target/junit-xml"	Directory report files are written to. Relative paths resolve against the project root, not the working directory.

:junit-xml {:output-dir "target/junit-xml"}

Requirements

Component	Version	How it was established
Leiningen	2.10.0 or newer	Lowest release the plugin is exercised on
Clojure, in the project under test	1.9 or newer	Hard floor — 1.8 fails to compile
Java, in the project under test	8 or newer	Full run verified on 8u482
Runtime dependencies added to your project	none

These are measured, not assumed. Each was established by running the plugin, not by reading release notes, and the evidence is recorded below so the numbers can be rechecked rather than trusted.

Two Clojure versions are in play and only one is the plugin's own. The task half (leiningen.junit-xml and impl.config) runs on Leiningen's bundled Clojure and needs only 1.5. The reporting half is loaded into your project's JVM and runs on your Clojure, so it declares no Clojure dependency and stays syntax-compatible with 1.9, with no 1.12-only reader syntax anywhere under src/com/github/robinlahtinen/. CI loads those namespaces against 1.9, 1.10, 1.11 and 1.12 on every push.

The task

Task	lein junit-xml
Arguments	identical to lein test: namespaces, test file paths, :selector keywords
Exit code	0 when the suite passes, 1 otherwise
Side effects	writes one file per test namespace under :output-dir; nothing else

XML contract

One file per test namespace, named TEST-<namespace>.xml. Characters outside [A-Za-z0-9._-] in the namespace become _ so the name is valid on Windows; the unmodified name stays in the name attribute. The root element is always <testsuite>; no <testsuites> wrapper is emitted, matching JUnit.

<testsuite>

Attributes, in the order JUnit writes them:

Attribute	Value
name	the test namespace
tests	total cases, including skipped ones
skipped	cases that did not run
failures	cases with at least one failed assertion
errors	cases that threw
time	wall-clock seconds, three decimals, always . as the separator
hostname	the reporting host, or <unknown host> if lookup fails
timestamp	suite start as an ISO-8601 UTC instant, e.g. 2026-09-20T16:18:05Z

Child order is (properties?, testcase*, system-out?, system-err?).

<testcase>

Attribute	Value
name	the deftest var name
classname	the fully-qualified namespace
time	wall-clock seconds, three decimals

Child order is (skipped?, error*, failure*).

classname drives the whole Package → Class → Test tree in Jenkins, which splits it at the last dot. A single-segment namespace therefore lands under Jenkins' (root) package; that is an accurate reflection of your namespace, and no package is invented to avoid it.

Result elements

Element	Attributes	Body
<failure>	message	expected form, actual form, and file:line
<error>	message, type (the exception class)	the full stack trace
<skipped>	none	the reason

<skipped> carries no message attribute: the schema types it as a simple type, so an attribute there is invalid. Jenkins falls back to the element's text, which is also what JUnit writes.

Aggregates count cases, not assertions

A deftest containing three failing is forms is one failure carrying three <failure> children. This matches JUnit, where a test method is a single result regardless of how many assertions it makes.

<properties>

A curated three: clojure.version, java.version, os.name. JUnit dumps the entire System.getProperties(), which leaks the build environment into every file; Jenkins discards them altogether unless the job opts in with keepProperties.

Character handling

Every string entering a document passes through one filter.

• Characters outside XML 1.0's Char production, defined as #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF], are replaced with U+FFFD. This covers ESC from ANSI colour output, NUL, other control bytes, non-characters, and unpaired surrogates.
• & < > are escaped in text; & < > " in attribute values.
• Newlines, carriage returns and tabs in attribute values are escaped numerically (
, 
, 	) so multi-line failure messages survive attribute-value normalisation.
• A ]]> inside a CDATA payload is split across two adjacent sections so it cannot terminate the section early.

This matters because Jenkins parses with a strict SAX reader and replaces an entire unparseable suite with a synthetic red [failed-to-read] case. One bad byte does not degrade a report; it destroys it.

Deliberate deviations from JUnit 6.2.0

#	JUnit writes	We write	Why
1	timestamp as a zone-less local date-time	an explicit UTC instant ending in Z	Jenkins appends Z to a zone-less value and reads it as UTC, shifting every suite start by the agent's offset
2	several <system-out> elements per case	exactly one	Jenkins reads only the first and silently discards the rest
3	<failure> before <error>	<error> before <failure>	the schema sequence is ordered; JUnit's order is invalid when a case has both, and Jenkins is order-insensitive either way
4	every system property	three	size and environment leakage, for data Jenkins discards by default
5	time via NumberFormat(Locale.US), grouping enabled	%.3f with Locale/ROOT	a grouping comma above 1000 seconds is invalid against the Surefire schema and breaks non-Jenkins consumers

Schema conformance

Reports are validated in CI against dev-resources/jenkins-junit.xsd, the schema junit-framework's own XmlReportAssertions validates every legacy report against.

dev-resources/surefire-test-report-3.0.2.xsd is not a second gate, and cannot be: it permits no timestamp and no hostname on <testsuite> and declares no anyAttribute, so JUnit 6.2.0's own output is invalid against it. Dropping those attributes to satisfy it would lose data Jenkins actually uses. The common subset is asserted instead, and the divergence is itself covered by a test so it is not later "fixed" in the wrong direction.

This is also why no assertions, file or line attributes appear on <testcase> even though they are common conventions elsewhere and the data is available: neither schema permits them.

Edge cases and limits

Situation	Behaviour
A namespace with no tests	A file is still written, with tests="0". Jenkins discards suites with no cases, so it will not appear there.
A :once fixture throws	The error is recorded as an initializationError case and the suite is written. Tests after the fixture never ran and are absent.
:monkeypatch-clojure-test false	Still supported; the plugin owns the failure path rather than relying on Leiningen's catcher.
A compile error in any test namespace	No files at all. Leiningen requires every test namespace before running anything, so the run aborts before a result exists.
The same namespace run twice in one JVM	Each run reports independently; per-run state resets on each invocation.
Output written to System/out directly	Not captured. See below.
Leiningen's own lein test :only … failure hints	Captured into <system-out>. Leiningen prints them with println, so they go to the same stream as your test output. Filtering them would mean matching on their exact wording, which is more fragile than reporting honestly what was printed.
Output from other threads	Not captured; *out* rebinding is thread-local.
Duplicate test names	Emitted as-is. Jenkins keeps both and disambiguates only their URLs.
A namespace defining test-ns-hook	Degraded. clojure.test bypasses test-var entirely there, so no per-test boundaries are reported: passing tests do not appear, and each failure becomes its own initializationError case. The suite is still written and still valid. test-ns-hook is also incompatible with fixtures, so this is rare.

Why System/out is not captured

System/setOut does not redirect Clojure's *out*, whose root writer is constructed over System.out when the runtime initialises. Capturing both would require System/setOut and alter-var-root on #'*out*, which is process-global and unsafe under :eval-in :leiningen or any parallel runner. The plugin takes the safe side.

Error states

Configuration errors throw ex-info before the project JVM starts, carrying:

{:com.github.robinlahtinen.lein-junit-xml/error   <category>
 :com.github.robinlahtinen.lein-junit-xml/context :com.github.robinlahtinen.lein-junit-xml/junit-xml
 ...}

Category	Raised when
:com.github.robinlahtinen.lein-junit-xml/invalid-type	:junit-xml is not a map, or :output-dir is not a string
:com.github.robinlahtinen.lein-junit-xml/invalid-value	:output-dir is blank
:com.github.robinlahtinen.lein-junit-xml/unsupported	an unrecognised key is present under :junit-xml

Errors inside the reporting path never propagate. They are printed to System/err prefixed with com.github.robinlahtinen/lein-junit-xml: and swallowed, because a bug in a reporter must not change whether your tests pass.

Internal data shapes

The suite value, produced by com.github.robinlahtinen.lein-junit-xml.impl.collect and consumed by com.github.robinlahtinen.lein-junit-xml.impl.xml:

{:name       "my.app.core-test"                                   ; namespace, as a string
 :timestamp  1758394685000                                        ; epoch millis, suite start
 :duration   1234                                                 ; millis
 :hostname   "build-07"
 :properties {"clojure.version" "1.12.6"}
 :out        "captured stdout"                                    ; absent when empty
 :err        "captured stderr"                                    ; absent when empty
 :cases      [{:name      "adds-test"
               :classname "my.app.core-test"
               :duration  12
               :results   [{:type    :fail                        ; :fail | :error | :skipped
                            :message "expected: (= 1 2)"
                            :class   "java.lang.RuntimeException" ; :error only
                            :detail  "expected/actual, or a stack trace"}]}]}

An empty :results vector means the case passed.