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Catalog / @effect/sql-pg / Testing Patterns
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Testing Patterns

Test setup with testcontainers, layer composition, and test utilities

testingtestcontainersvitestlayers

Testing Patterns

Overview

The package tests use @testcontainers/postgresql to spin up real PostgreSQL instances in Docker. The test utilities demonstrate idiomatic Effect layer composition for test environments.

Key Concepts

PgContainer Service

test/utils.ts defines a PgContainer service using Effect.Service:

export class PgContainer extends Effect.Service<PgContainer>()("test/PgContainer", {
  scoped: Effect.acquireRelease(
    Effect.tryPromise({
      try: () => new PostgreSqlContainer("postgres:alpine").start(),
      catch: (cause) => new ContainerError({ cause })
    }),
    (container) => Effect.promise(() => container.stop())
  )
}) {}

The container is started once and shared across tests via the layer system.

Three Test Layer Variants

ClientLive - Basic client from container URL:

static ClientLive = Layer.unwrapEffect(
  Effect.gen(function*() {
    const container = yield* PgContainer
    return PgClient.layer({
      url: Redacted.make(container.getConnectionUri())
    })
  })
).pipe(Layer.provide(PgContainer.Default))

ClientTransformLive - Client with snake/camel transforms:

static ClientTransformLive = Layer.unwrapEffect(
  Effect.gen(function*() {
    const container = yield* PgContainer
    return PgClient.layer({
      url: Redacted.make(container.getConnectionUri()),
      transformResultNames: String.snakeToCamel,
      transformQueryNames: String.camelToSnake
    })
  })
).pipe(Layer.provide(PgContainer.Default))

ClientFromPoolLive - Client from external pool:

static ClientFromPoolLive = Layer.unwrapEffect(
  Effect.gen(function*() {
    const container = yield* PgContainer
    const acquire = Effect.acquireRelease(
      Effect.sync(() => new Pg.Pool({
        connectionString: container.getConnectionUri()
      })),
      (pool) => Effect.promise(() => pool.end())
    )
    return PgClient.layerFromPool({ acquire, ...transforms })
  })
).pipe(Layer.provide(PgContainer.Default))

Test Structure with @effect/vitest

Tests use it.layer() to provide the test layer, then it.effect() for individual Effect-based tests:

it.layer(PgContainer.ClientLive, { timeout: "30 seconds" })("PgClient", (it) => {
  it.effect("insert helper", () =>
    Effect.gen(function*() {
      const sql = yield* PgClient.PgClient
      const [query, params] = sql`INSERT INTO people ${
        sql.insert({ name: "Tim", age: 10 })
      }`.compile()
      expect(query).toEqual(`INSERT INTO people ("name","age") VALUES ($1,$2)`)
    }))
})

TaggedError for Container Failures

export class ContainerError extends Data.TaggedError("ContainerError")<{
  cause: unknown
}> {}

Vitest Configuration

The vitest config is minimal, extending a shared monorepo config:

// vitest.config.ts merges with ../../vitest.shared.js

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