Add integration tests using testcontainers-scala

[Copilot]

Adds end-to-end integration tests for the ETL pipeline using testcontainers to validate database extraction, streaming, and error handling.

Changes

Dependencies (build.sbt)

• testcontainers-scala-scalatest 0.41.4
• testcontainers-scala-postgresql 0.41.4
• cats-effect-testing-scalatest 1.5.0

Integration Test Suite (EtlPipelineIntegrationSpec.scala)

• PostgreSQL extraction with 10-record validation
• Empty result set handling
• Batch streaming verification (configurable batch size)
• Uses PostgreSQL testcontainer for isolated testing
• AsyncIOSpec for proper Cats Effect IO testing

Documentation

• Added integration test section to README with Docker requirement
• Updated PROJECT_SUMMARY with test counts and current dependency versions

Example

"EtlPipeline" should "successfully extract data from PostgreSQL" in {
  withContainers { postgres =>
    (for {
      _ <- setupTestData(postgres)
      config = createTestConfig(postgres)
      _ <- DatabaseConnection.createTransactor[IO](config.database).use { xa =>
        for {
          data <- DataRepository[IO](xa)
            .streamData(config.etl.query, config.etl.batchSize)
            .compile.toList
          _ <- IO {
            data.size should be(10)
            data.head.name shouldBe "Product A"
          }
        } yield succeed
      }
    } yield succeed).unsafeToFuture()
  }
}

Test Results: 9 tests passing (6 unit + 3 integration)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add integration tests using testcontainers</issue_title>
<issue_description>* use testcontainers scala</issue_description>

<agent_instructions>Test end 2 end application logic using testcontainers-scala.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Add integration tests using testcontainers #8

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