This is an automated email from the ASF dual-hosted git repository.
olamy pushed a commit to branch master
in repository
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The following commit(s) were added to refs/heads/master by this push:
new 8b862ca Test-jar type dependencies fail to be resolved during
checksum calculation with -f builds (#468)
8b862ca is described below
commit 8b862ca42cba2d8a7c833e86d21234e4ff166ad9
Author: Olivier Lamy <[email protected]>
AuthorDate: Tue Mar 24 07:32:22 2026 +1000
Test-jar type dependencies fail to be resolved during checksum calculation
with -f builds (#468)
Signed-off-by: Olivier Lamy <[email protected]>
---
.../buildcache/checksum/MavenProjectInput.java | 14 ++-
.../its/projecttypes/SingleModuleTestJarTest.java | 108 +++++++++++++++++++++
.../p20-single-module-testjar/.mvn/extensions.xml | 26 +++++
.../.mvn/maven-build-cache-config.xml | 28 ++++++
.../module-consumer/pom.xml | 47 +++++++++
.../caching/test/p20/consumer/ConsumerApp.java | 31 ++++++
.../caching/test/p20/consumer/ConsumerTest.java | 31 ++++++
.../module-producer/pom.xml | 49 ++++++++++
.../caching/test/p20/producer/ProducerLib.java | 29 ++++++
.../caching/test/p20/producer/TestHelper.java | 29 ++++++
.../p20-single-module-testjar/pom.xml | 39 ++++++++
.../p20-single-module-testjar/readme.md | 31 ++++++
12 files changed, 460 insertions(+), 2 deletions(-)
diff --git
a/src/main/java/org/apache/maven/buildcache/checksum/MavenProjectInput.java
b/src/main/java/org/apache/maven/buildcache/checksum/MavenProjectInput.java
index 4f05eb3..8f31237 100644
--- a/src/main/java/org/apache/maven/buildcache/checksum/MavenProjectInput.java
+++ b/src/main/java/org/apache/maven/buildcache/checksum/MavenProjectInput.java
@@ -836,11 +836,21 @@ private DigestItem resolveArtifact(final Dependency
dependency)
return DtoUtils.createDigestedFile(artifact, hash);
}
+ // Handle special dependency types that have implicit classifiers
+ String classifier = dependency.getClassifier();
+ String extension = null;
+
+ // test-jar type requires "tests" classifier and "jar" extension
+ if ("test-jar".equals(dependency.getType()) && (classifier == null ||
classifier.isEmpty())) {
+ classifier = "tests";
+ extension = "jar";
+ }
+
org.eclipse.aether.artifact.Artifact dependencyArtifact = new
org.eclipse.aether.artifact.DefaultArtifact(
dependency.getGroupId(),
dependency.getArtifactId(),
- dependency.getClassifier(),
- null,
+ classifier,
+ extension,
dependency.getVersion(),
new DefaultArtifactType(dependency.getType()));
ArtifactRequest artifactRequest = new
ArtifactRequest().setArtifact(dependencyArtifact);
diff --git
a/src/test/java/org/apache/maven/buildcache/its/projecttypes/SingleModuleTestJarTest.java
b/src/test/java/org/apache/maven/buildcache/its/projecttypes/SingleModuleTestJarTest.java
new file mode 100644
index 0000000..2316b2a
--- /dev/null
+++
b/src/test/java/org/apache/maven/buildcache/its/projecttypes/SingleModuleTestJarTest.java
@@ -0,0 +1,108 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.buildcache.its.projecttypes;
+
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+import org.apache.maven.buildcache.its.CacheITUtils;
+import org.apache.maven.buildcache.its.MavenSetup;
+import org.apache.maven.buildcache.its.ReferenceProjectBootstrap;
+import org.apache.maven.it.Verifier;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.parallel.ResourceLock;
+import org.junit.jupiter.api.parallel.Resources;
+
+/**
+ * Verifies that single module builds with {@code mvn -f <submodule>} work
correctly when the
+ * submodule depends on test-jar artifacts from other modules (reproduces
issue #467).
+ *
+ * <p>The issue occurs when building a single module that depends on a
test-jar artifact:
+ * the build cache extension fails to resolve the test-jar dependency from the
local repository
+ * because {@code session.getAllProjects()} only contains the single module
being built.
+ *
+ * <p>Uses P20 ({@code p20-single-module-testjar}) which includes:
+ * - {@code module-producer}: produces both regular jar and test-jar
+ * - {@code module-consumer}: depends on test-jar from producer
+ *
+ * <p>Test sequence:
+ * 1. Full reactor build to populate local repository and cache
+ * 2. Single module build of consumer (should succeed with fixed resolution
logic)
+ */
+@Tag("smoke")
+@ResourceLock(Resources.SYSTEM_PROPERTIES)
+class SingleModuleTestJarTest {
+
+ @BeforeAll
+ static void setUpMaven() throws Exception {
+ MavenSetup.configureMavenHome();
+ }
+
+ @Test
+ void singleModuleBuildWithTestJarDependency() throws Exception {
+ Path p20 =
Paths.get("src/test/projects/reference-test-projects/p20-single-module-testjar")
+ .toAbsolutePath();
+ Verifier verifier = ReferenceProjectBootstrap.prepareProject(p20,
"SingleModuleTestJarTest");
+ verifier.setAutoclean(false);
+
+ // Build 1: Full reactor build to populate local repository and cache
+ // This should work (both modules built together)
+ verifier.setLogFileName("../log-full-reactor.txt");
+ verifier.executeGoal("install");
+ verifier.verifyErrorFreeLog();
+ verifier.verifyTextInLog(CacheITUtils.CACHE_SAVED);
+
+ // Build 2: Single module build of consumer (the critical test)
+ // Before fix: this would fail with ArtifactResolutionException for
test-jar
+ // After fix: this should succeed by resolving test-jar from local
repository
+ verifier.setLogFileName("../log-single-module.txt");
+ verifier.addCliOption("-f");
+ verifier.addCliOption("module-consumer");
+ verifier.executeGoal("install");
+ verifier.verifyErrorFreeLog();
+ // Should be able to resolve test-jar dependency and calculate
checksums successfully
+ verifier.verifyTextInLog("Going to calculate checksum for project");
+ }
+
+ @Test
+ void singleModuleBuildWithCacheDisabledShouldWork() throws Exception {
+ Path p20 =
Paths.get("src/test/projects/reference-test-projects/p20-single-module-testjar")
+ .toAbsolutePath();
+ Verifier verifier = ReferenceProjectBootstrap.prepareProject(p20,
"SingleModuleTestJarTestDisabled");
+ verifier.setAutoclean(false);
+
+ // Build 1: Full reactor build to populate local repository
+ verifier.setLogFileName("../log-full-reactor-disabled.txt");
+ verifier.setSystemProperty("maven.build.cache.enabled", "false");
+ verifier.executeGoal("install");
+ verifier.verifyErrorFreeLog();
+ verifier.verifyTextInLog("Cache disabled by command line flag");
+
+ // Build 2: Single module build with cache disabled (control test -
should always work)
+ verifier.setLogFileName("../log-single-module-disabled.txt");
+ verifier.addCliOption("-f");
+ verifier.addCliOption("module-consumer");
+ verifier.setSystemProperty("maven.build.cache.enabled", "false");
+ verifier.executeGoal("install");
+ verifier.verifyErrorFreeLog();
+ verifier.verifyTextInLog("Cache is DISABLED on project level");
+ }
+}
diff --git
a/src/test/projects/reference-test-projects/p20-single-module-testjar/.mvn/extensions.xml
b/src/test/projects/reference-test-projects/p20-single-module-testjar/.mvn/extensions.xml
new file mode 100644
index 0000000..d28f29c
--- /dev/null
+++
b/src/test/projects/reference-test-projects/p20-single-module-testjar/.mvn/extensions.xml
@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements. See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership. The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied. See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+<extensions>
+ <extension>
+ <groupId>org.apache.maven.extensions</groupId>
+ <artifactId>maven-build-cache-extension</artifactId>
+ <version>${projectVersion}</version>
+ </extension>
+</extensions>
diff --git
a/src/test/projects/reference-test-projects/p20-single-module-testjar/.mvn/maven-build-cache-config.xml
b/src/test/projects/reference-test-projects/p20-single-module-testjar/.mvn/maven-build-cache-config.xml
new file mode 100644
index 0000000..6f9399c
--- /dev/null
+++
b/src/test/projects/reference-test-projects/p20-single-module-testjar/.mvn/maven-build-cache-config.xml
@@ -0,0 +1,28 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements. See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership. The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied. See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+<cache xmlns="http://maven.apache.org/BUILD-CACHE-CONFIG/1.2.0";
+ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
+ xsi:schemaLocation="http://maven.apache.org/BUILD-CACHE-CONFIG/1.2.0
+ https://maven.apache.org/xsd/build-cache-config-1.2.0.xsd";>
+ <configuration>
+ <enabled>true</enabled>
+ <hashAlgorithm>XX</hashAlgorithm>
+ </configuration>
+</cache>
diff --git
a/src/test/projects/reference-test-projects/p20-single-module-testjar/module-consumer/pom.xml
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-consumer/pom.xml
new file mode 100644
index 0000000..83c9ca7
--- /dev/null
+++
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-consumer/pom.xml
@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements. See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership. The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied. See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0";
+ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
+ xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd";>
+ <modelVersion>4.0.0</modelVersion>
+
+ <parent>
+ <groupId>org.apache.maven.caching.test.p20</groupId>
+ <artifactId>p20-single-module-testjar</artifactId>
+ <version>1.0-SNAPSHOT</version>
+ </parent>
+
+ <artifactId>module-consumer</artifactId>
+
+ <dependencies>
+ <dependency>
+ <groupId>org.apache.maven.caching.test.p20</groupId>
+ <artifactId>module-producer</artifactId>
+ <version>${project.version}</version>
+ </dependency>
+ <dependency>
+ <groupId>org.apache.maven.caching.test.p20</groupId>
+ <artifactId>module-producer</artifactId>
+ <version>${project.version}</version>
+ <scope>test</scope>
+ <type>test-jar</type>
+ </dependency>
+ </dependencies>
+</project>
\ No newline at end of file
diff --git
a/src/test/projects/reference-test-projects/p20-single-module-testjar/module-consumer/src/main/java/org/apache/maven/caching/test/p20/consumer/ConsumerApp.java
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-consumer/src/main/java/org/apache/maven/caching/test/p20/consumer/ConsumerApp.java
new file mode 100644
index 0000000..8276886
--- /dev/null
+++
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-consumer/src/main/java/org/apache/maven/caching/test/p20/consumer/ConsumerApp.java
@@ -0,0 +1,31 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.caching.test.p20.consumer;
+
+import org.apache.maven.caching.test.p20.producer.ProducerLib;
+
+/**
+ * P20 module-consumer: main app using producer lib.
+ */
+public class ConsumerApp {
+
+ public static void main(String[] args) {
+ System.out.println(ProducerLib.greeting());
+ }
+}
\ No newline at end of file
diff --git
a/src/test/projects/reference-test-projects/p20-single-module-testjar/module-consumer/src/test/java/org/apache/maven/caching/test/p20/consumer/ConsumerTest.java
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-consumer/src/test/java/org/apache/maven/caching/test/p20/consumer/ConsumerTest.java
new file mode 100644
index 0000000..b5aaddc
--- /dev/null
+++
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-consumer/src/test/java/org/apache/maven/caching/test/p20/consumer/ConsumerTest.java
@@ -0,0 +1,31 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.caching.test.p20.consumer;
+
+import org.apache.maven.caching.test.p20.producer.TestHelper;
+
+/**
+ * P20 module-consumer: test class that uses test-jar dependency from producer.
+ */
+public class ConsumerTest {
+
+ public static void main(String[] args) {
+ System.out.println(TestHelper.testGreeting());
+ }
+}
\ No newline at end of file
diff --git
a/src/test/projects/reference-test-projects/p20-single-module-testjar/module-producer/pom.xml
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-producer/pom.xml
new file mode 100644
index 0000000..b48123e
--- /dev/null
+++
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-producer/pom.xml
@@ -0,0 +1,49 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements. See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership. The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied. See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0";
+ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
+ xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd";>
+ <modelVersion>4.0.0</modelVersion>
+
+ <parent>
+ <groupId>org.apache.maven.caching.test.p20</groupId>
+ <artifactId>p20-single-module-testjar</artifactId>
+ <version>1.0-SNAPSHOT</version>
+ </parent>
+
+ <artifactId>module-producer</artifactId>
+
+ <build>
+ <plugins>
+ <plugin>
+ <groupId>org.apache.maven.plugins</groupId>
+ <artifactId>maven-jar-plugin</artifactId>
+ <version>3.4.2</version>
+ <executions>
+ <execution>
+ <goals>
+ <goal>test-jar</goal>
+ </goals>
+ </execution>
+ </executions>
+ </plugin>
+ </plugins>
+ </build>
+</project>
\ No newline at end of file
diff --git
a/src/test/projects/reference-test-projects/p20-single-module-testjar/module-producer/src/main/java/org/apache/maven/caching/test/p20/producer/ProducerLib.java
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-producer/src/main/java/org/apache/maven/caching/test/p20/producer/ProducerLib.java
new file mode 100644
index 0000000..b8f10dc
--- /dev/null
+++
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-producer/src/main/java/org/apache/maven/caching/test/p20/producer/ProducerLib.java
@@ -0,0 +1,29 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.caching.test.p20.producer;
+
+/**
+ * P20 module-producer: main library class.
+ */
+public class ProducerLib {
+
+ public static String greeting() {
+ return "Hello from producer lib";
+ }
+}
\ No newline at end of file
diff --git
a/src/test/projects/reference-test-projects/p20-single-module-testjar/module-producer/src/test/java/org/apache/maven/caching/test/p20/producer/TestHelper.java
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-producer/src/test/java/org/apache/maven/caching/test/p20/producer/TestHelper.java
new file mode 100644
index 0000000..93829c3
--- /dev/null
+++
b/src/test/projects/reference-test-projects/p20-single-module-testjar/module-producer/src/test/java/org/apache/maven/caching/test/p20/producer/TestHelper.java
@@ -0,0 +1,29 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.caching.test.p20.producer;
+
+/**
+ * P20 module-producer: test helper class exported via test-jar for reuse in
other modules' tests.
+ */
+public class TestHelper {
+
+ public static String testGreeting() {
+ return "Hello from producer test helper";
+ }
+}
\ No newline at end of file
diff --git
a/src/test/projects/reference-test-projects/p20-single-module-testjar/pom.xml
b/src/test/projects/reference-test-projects/p20-single-module-testjar/pom.xml
new file mode 100644
index 0000000..6e6e5ca
--- /dev/null
+++
b/src/test/projects/reference-test-projects/p20-single-module-testjar/pom.xml
@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements. See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership. The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied. See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0";
+ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
+ xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd";>
+ <modelVersion>4.0.0</modelVersion>
+
+ <groupId>org.apache.maven.caching.test.p20</groupId>
+ <artifactId>p20-single-module-testjar</artifactId>
+ <version>1.0-SNAPSHOT</version>
+ <packaging>pom</packaging>
+
+ <modules>
+ <module>module-producer</module>
+ <module>module-consumer</module>
+ </modules>
+
+ <properties>
+ <maven.compiler.release>17</maven.compiler.release>
+ <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+ </properties>
+</project>
\ No newline at end of file
diff --git
a/src/test/projects/reference-test-projects/p20-single-module-testjar/readme.md
b/src/test/projects/reference-test-projects/p20-single-module-testjar/readme.md
new file mode 100644
index 0000000..053748c
--- /dev/null
+++
b/src/test/projects/reference-test-projects/p20-single-module-testjar/readme.md
@@ -0,0 +1,31 @@
+# P20: Single Module Test-jar Dependencies
+
+P20 tests building a single module with `mvn -f <submodule>` when that module
depends on a test-jar artifact from another module.
+
+## Project Structure
+
+```
+p20-single-module-testjar/
+ ├── module-producer/ (produces test-jar artifact)
+ └── module-consumer/ (depends on test-jar from producer)
+```
+
+## Test Scenario
+
+- `module-producer`: produces both regular jar and test-jar
+- `module-consumer`: depends on both regular jar and test-jar from producer
+
+## Key Test Case
+
+The critical test is: **Can `mvn -f module-consumer clean install` succeed
when the build cache extension is enabled?**
+
+- Full reactor builds (`mvn clean install`) should always work
+- Single module builds (`mvn -f module-consumer clean install`) failed in
issue #467 due to test-jar resolution problems
+- The build cache extension could not resolve test-jar dependencies even when
they existed in local repository
+
+## Resolution Testing
+
+This project validates that the build cache extension can properly:
+1. Resolve test-jar dependencies from local repository in single module builds
+2. Calculate checksums for projects with test-jar dependencies
+3. Handle the case where `session.getAllProjects()` only contains the single
module being built
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