add a base case test for tracking source files with a single source p…

…er generated

context: #836 (comment)

compiler/src/test/java/com/squareup/anvil/compiler/codegen/CodeGenerationExtensionTest.kt

@@ -5,6 +5,7 @@ import com.squareup.anvil.compiler.compile
 import com.squareup.anvil.compiler.internal.testing.SimpleCodeGenerator
 import com.squareup.anvil.compiler.internal.testing.SimpleSourceFileTrackingBehavior.NO_SOURCE_TRACKING
 import com.squareup.anvil.compiler.internal.testing.SimpleSourceFileTrackingBehavior.TRACKING_WITH_NO_SOURCES
+import com.squareup.anvil.compiler.internal.testing.SimpleSourceFileTrackingBehavior.TRACK_SOURCE_FILES
 import com.squareup.anvil.compiler.internal.testing.simpleCodeGenerator
 import com.squareup.anvil.compiler.isError
 import com.tschuchort.compiletesting.KotlinCompilation.ExitCode.COMPILATION_ERROR
@@ -203,6 +204,41 @@ class CodeGenerationExtensionTest {
     }
   }
 
+  @Test fun `a code generator that tracks an a single source per generated file can use trackSourceFiles`() {
+
+    val codeGenerator = simpleCodeGenerator(TRACK_SOURCE_FILES) { clazz ->
+
+      if (clazz.shortName == "Abc") {
+        return@simpleCodeGenerator null
+      }
+
+      """
+        package com.squareup.test
+          
+        class Abc
+      """.trimIndent()
+    }
+
+    //language=kotlin
+    val componentInterface = """
+      package com.squareup.test
+
+      interface ComponentInterface
+    """.trimIndent()
+
+    compile(
+      componentInterface,
+      codeGenerators = listOf(codeGenerator),
+      trackSourceFiles = true,
+    ) {
+      assertThat(codeGenerator.isApplicableCalls).isEqualTo(1)
+      assertThat(codeGenerator.getGenerateCallsForInputFileContent(componentInterface)).isEqualTo(1)
+
+      assertThat(exitCode).isEqualTo(OK)
+      assertThat(classLoader.loadClass("com.squareup.test.Abc")).isNotNull()
+    }
+  }
+
   @Test
   fun `a code generator that does not track sources can compile with trackSourceFiles disabled`() {
     val codeGenerator = simpleCodeGenerator(NO_SOURCE_TRACKING) { clazz ->