Add a unit test for the code generator.

anvilcodegen/build.gradle

@@ -9,13 +9,18 @@ tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {
 }
 
 dependencies {
-    implementation project(':lib.daggerscopes')
     api "com.squareup.anvil:compiler-api:2.4.0"
+    implementation project(':lib.daggerscopes')
     implementation "com.squareup.anvil:compiler-utils:2.4.0"
     implementation "com.squareup:kotlinpoet:1.10.2"
     implementation 'com.google.dagger:dagger:2.42'
     implementation 'com.squareup.retrofit2:retrofit:2.9.0'
     implementation project(':lib.daggerscopes')
+
     compileOnly "com.google.auto.service:auto-service-annotations:1.0.1"
     kapt "com.google.auto.service:auto-service:1.0.1"
+
+    testImplementation testFixtures("com.squareup.anvil:compiler-utils:2.4.0")
+    testImplementation "com.google.truth:truth:1.1.3"
+    testImplementation "junit:junit:4.13.2"
 }

anvilcodegen/src/test/java/com/gpeal/droidconanvilsample/anvilcompilers/ContributesApiCodeGeneratorTest.kt

@@ -0,0 +1,32 @@
+package com.gpeal.droidconanvilsample.anvilcompilers
+
+import com.google.common.truth.Truth.assertThat
+import com.squareup.anvil.compiler.internal.testing.compileAnvil
+import com.tschuchort.compiletesting.KotlinCompilation.ExitCode.OK
+import dagger.Provides
+import dagger.Reusable
+import org.junit.Test
+
+class ContributesApiCodeGeneratorTest {
+
+    @Test fun `a dagger module is generated`() {
+        compileAnvil(
+            """
+                package com.test
+                
+                import com.gpeal.droidconanvilsample.lib.daggerscopes.ContributesApi
+
+                @ContributesApi
+                interface TestApi
+            """
+        ) {
+            assertThat(exitCode).isEqualTo(OK)
+
+            val clazz = classLoader.loadClass("com.test.TestApi_Module")
+            val providerMethod = clazz.declaredMethods.single()
+
+            assertThat(providerMethod.returnType).isEqualTo(classLoader.loadClass("com.test.TestApi"))
+            assertThat(providerMethod.annotations.map { it.annotationClass }).containsExactly(Provides::class, Reusable::class)
+        }
+    }
+}