Make the tests faster

scripts/test

@@ -2,4 +2,4 @@
 
 npm_bin=$(npm bin)
 
-$npm_bin/jest $@
+$npm_bin/jest --maxWorkers 3 $@

src/__tests__/utils/createTestInParallel.ts

@@ -0,0 +1,31 @@
+/**
+ * Runs all of the tests declared with this funcion in a file in parallel. This
+ * breaks any `beforeEach` and `afterEach` functions, but any `beforeAll` and
+ * `afterAll` functions should work.
+ *
+ * This function will break the timing numbers in the Jest console.
+ */
+export default function createTestInParallel(): (name: string, fn: () => void | Promise<void>) => void {
+  // All of the test functions. We collect them in a single array so that we can
+  // call them all at once.
+  const testFns: Array<() => void | Promise<void>> = []
+
+  // The promised results of calling all of our test functions. The single serial
+  // tests will await these values.
+  let testResults: Array<Promise<void>> | undefined
+
+  return (name: string, fn: () => void | Promise<void>): void => {
+    // Add the test function and record its position.
+    const index = testFns.length
+    testFns.push(fn)
+
+    test(name, async () => {
+      // If the tests have not yet been run then run all of our tests.
+      if (!testResults) {
+        testResults = testFns.map(testFn => Promise.resolve(testFn()))
+      }
+      // Await the result.
+      await testResults[index]
+    })
+  }
+}

src/postgres/__tests__/fixtures/withPgClient.ts → src/__tests__/utils/withPgClient.ts

@@ -7,8 +7,10 @@ import kitchenSinkSchemaSql from './kitchenSinkSchemaSql'
  * client. The client will be connected from the pool at the start of the test,
  * and released back at the end. All changes will be rolled back.
  */
-export default function withPgClient (fn: (client: Client) => void | Promise<void>): () => Promise<void> {
-  return async (): Promise<void> => {
+export default function withPgClient <T>(fn: (client: Client) => T | Promise<T>): () => Promise<T> {
+  return async (): Promise<T> => {
+    let result: T | undefined
+
     // Connect a client from our pool and begin a transaction.
     const client = await pgPool.connect()
 
@@ -27,8 +29,11 @@ export default function withPgClient (fn: (client: Client) => void | Promise<voi
       await client.query(await kitchenSinkSchemaSql)
     }
     catch (error) {
-      // tslint:disable-next-line no-console
-      console.error(error.stack || error)
+      // Release the client if an error was thrown.
+      await client.query('rollback')
+      client.release()
+      // Log the error for debugging purposes.
+      console.error(error.stack || error) // tslint:disable-line no-console
       throw error
     }
 
@@ -37,13 +42,17 @@ export default function withPgClient (fn: (client: Client) => void | Promise<voi
 
     // Try to run our test, if it fails we still want to cleanup the client.
     try {
-      await fn(client)
+      result = await fn(client)
     }
     // Always rollback our changes and release the client, even if the test
     // fails.
     finally {
       await client.query('rollback')
       client.release()
     }
+
+    // We will always define our result in the above block. It appears that
+    // TypeScript cannot detect that so we need to tell it with the bang.
+    return result!
   }
 }