test: add sadly non-failing test case for duplicate Android resource issue.

src/functionalTest/groovy/com/autonomousapps/android/ResSpec.groovy

@@ -4,9 +4,11 @@ package com.autonomousapps.android
 
 import com.autonomousapps.android.projects.*
 import org.gradle.testkit.runner.TaskOutcome
+import spock.lang.PendingFeature
 
 import static com.autonomousapps.advice.truth.BuildHealthSubject.buildHealth
-import static com.autonomousapps.utils.Runner.build
+import static com.autonomousapps.kit.GradleBuilder.build
+import static com.autonomousapps.kit.GradleBuilder.buildAndFail
 import static com.google.common.truth.Truth.assertAbout
 
 @SuppressWarnings("GroovyAssignabilityCheck")
@@ -203,4 +205,35 @@ final class ResSpec extends AbstractAndroidSpec {
     where:
     [gradleVersion, agpVersion] << gradleAgpMatrix()
   }
+
+  // TODO(tsr): this test case demonstrates (or more accurately: fails to demonstrate) any issue when multiple Android
+  //  libraries provide a resource with the same name, and the consumer side only references that resource in an XML
+  //  file (so there's no qualified reference in code for more accurate detection).
+  // See e.g. https://developer.android.com/studio/projects/android-library#Considerations for information on resource
+  //  merging; and
+  // https://developer.android.com/reference/tools/gradle-api/8.3/null/com/android/build/api/dsl/CommonExtension#setResourcePrefix(kotlin.String)
+  //  for an AGP DSL that can help mitigate the problem (set unique prefixes everywhere and use them).
+  // This is annotated with `@PendingFeature` because the assertion is that the build fails (but the build succeeds). If
+  // there is ever any improvement in this scenario, this case will begin to really fail and then we can update the
+  // assertions.
+  @PendingFeature(reason = "https://github.com/autonomousapps/dependency-analysis-gradle-plugin/issues/1731")
+  def "handles duplicate res-by-res producers (#gradleVersion AGP #agpVersion)"() {
+    given:
+    def project = new ResByResProject(agpVersion)
+    gradleProject = project.gradleProject
+
+    when:
+    buildAndFail(gradleVersion, gradleProject.rootDir, 'buildHealth')
+    // The output is identical
+//    build(gradleVersion, gradleProject.rootDir, ':app:reason', '--id', ':res1')
+//    build(gradleVersion, gradleProject.rootDir, ':app:reason', '--id', ':res2')
+
+    then:
+    assertAbout(buildHealth())
+      .that(project.actualBuildHealth())
+      .isEquivalentIgnoringModuleAdviceAndWarnings(project.expectedBuildHealth)
+
+    where:
+    [gradleVersion, agpVersion] << gradleAgpMatrix()
+  }
 }

src/functionalTest/groovy/com/autonomousapps/android/projects/AbstractAndroidProject.groovy

@@ -110,6 +110,10 @@ abstract class AbstractAndroidProject extends AbstractProject {
     return AndroidManifest.appWithoutPackage(namespace)
   }
 
+  protected AndroidManifest appEmpty() {
+    return AndroidManifest.appEmpty()
+  }
+
   protected AndroidManifest libraryManifest(String namespace = DEFAULT_LIB_NAMESPACE) {
     return null
   }

src/functionalTest/groovy/com/autonomousapps/android/projects/ResByResProject.groovy

@@ -0,0 +1,92 @@
+// Copyright (c) 2026. Tony Robalik.
+// SPDX-License-Identifier: Apache-2.0
+package com.autonomousapps.android.projects
+
+import com.autonomousapps.kit.GradleProject
+import com.autonomousapps.kit.android.AndroidLayout
+import com.autonomousapps.kit.android.AndroidStringRes
+import com.autonomousapps.kit.android.AndroidSubproject
+import com.autonomousapps.model.ProjectAdvice
+
+import static com.autonomousapps.AdviceHelper.actualProjectAdvice
+import static com.autonomousapps.AdviceHelper.emptyProjectAdviceFor
+import static com.autonomousapps.kit.gradle.Dependency.project
+
+/**
+ * In this app project, there is a layout file that references a string resource by name (not fully-qualified, because
+ * XML). Two separate Android libraries provide this same resource. The project has `android.nonTransitiveRClass`
+ * enabled. Is this a problem?
+ */
+final class ResByResProject extends AbstractAndroidProject {
+
+  final GradleProject gradleProject
+  private final String agpVersion
+
+  ResByResProject(String agpVersion) {
+    super(agpVersion)
+    this.agpVersion = agpVersion
+    this.gradleProject = build()
+  }
+
+  private GradleProject build() {
+    return newAndroidGradleProjectBuilder(agpVersion)
+      .withAndroidSubproject('app') { app ->
+        app.withBuildScript { bs ->
+          bs.plugins(androidApp())
+          bs.android = defaultAndroidAppBlock(false)
+          bs.dependencies(
+            project('implementation', ':res1'),
+            project('implementation', ':res2'),
+          )
+        }
+        app.manifest = appEmpty()
+        app.layouts(
+          AndroidLayout
+            .named('string_layout.xml')
+            .withContent('''\
+            <?xml version="1.0" encoding="utf-8"?>
+            <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+              android:orientation="vertical"
+              android:layout_width="match_parent"
+              android:layout_height="match_parent">
+
+              <TextView
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:text="@string/common_ok" />
+            </LinearLayout>'''.stripIndent())
+        )
+      }
+      .withAndroidLibProject('res1') { lib ->
+        configureResLib(lib, 'res1')
+      }
+      .withAndroidLibProject('res2') { lib ->
+        configureResLib(lib, 'res2')
+      }
+      .write()
+  }
+
+  private void configureResLib(AndroidSubproject.Builder lib, String name) {
+    lib.withBuildScript { bs ->
+      bs.plugins(androidLib(false))
+      bs.android = defaultAndroidLibBlock(false, "com.example.$name")
+    }
+    lib.manifest = libraryManifest("com.example.$name")
+    lib.strings = new AndroidStringRes(
+      '''\
+        <resources>
+          <string name="common_ok">OK</string>
+        </resources>'''.stripIndent()
+    )
+  }
+
+  Set<ProjectAdvice> actualBuildHealth() {
+    return actualProjectAdvice(gradleProject)
+  }
+
+  final Set<ProjectAdvice> expectedBuildHealth = [
+    emptyProjectAdviceFor(':app'),
+    emptyProjectAdviceFor(':res1'),
+    emptyProjectAdviceFor(':res2'),
+  ]
+}

testkit/gradle-testkit-support/src/main/kotlin/com/autonomousapps/kit/android/AndroidLayout.kt

@@ -6,5 +6,21 @@ public class AndroidLayout(
   public val filename: String,
   public val content: String,
 ) {
+
   override fun toString(): String = content
+
+  public class Builder(private val name: String) {
+    public fun withContent(content: String): AndroidLayout {
+      return AndroidLayout(
+        filename = name,
+        content = content,
+      )
+    }
+  }
+
+  public companion object {
+    /** The [name] should be just the filename. The path (e.g., `src/main/res/layout/<name>`) is assumed. */
+    @JvmStatic
+    public fun named(name: String): Builder = Builder(name)
+  }
 }

testkit/gradle-testkit-support/src/main/kotlin/com/autonomousapps/kit/android/AndroidSubproject.kt

@@ -38,7 +38,7 @@ public class AndroidSubproject(
     public var styles: AndroidStyleRes? = null
     public var strings: AndroidStringRes? = null
     public var colors: AndroidColorRes? = null
-    public var layouts: List<AndroidLayout>? = null
+    public var layouts: MutableList<AndroidLayout> = mutableListOf()
     public val files: MutableList<File> = mutableListOf()
 
     // sub-builders
@@ -63,6 +63,10 @@ public class AndroidSubproject(
       }
     }
 
+    public fun layouts(vararg layouts: AndroidLayout) {
+      this.layouts.addAll(layouts.toMutableList())
+    }
+
     public fun withFile(path: String, content: String) {
       withFile(File(path, content))
     }