mrpowers / spark-fast-tests

Apache Spark test helper functions with pretty error messages

GitHub

spark-fast-tests

A fast, test framework independent Apache Spark testing helper library with beautifully formatted error messages!

Codacy Badge

For example, the assertSmallDatasetEquality method can be used to compare two Datasets (or two DataFrames).

val sourceDF = Seq(
  (1),
  (5)
).toDF("number")

val expectedDF = Seq(
  (1, "word"),
  (5, "word")
).toDF("number", "word")

assertSmallDataFrameEquality(sourceDF, expectedDF)
// throws a DatasetSchemaMismatch exception

The assertSmallDatasetEquality method can also be used to compare Datasets.

val sourceDS = Seq(
  Person("juan", 5),
  Person("bob", 1),
  Person("li", 49),
  Person("alice", 5)
).toDS

val expectedDS = Seq(
  Person("juan", 5),
  Person("frank", 10),
  Person("li", 49),
  Person("lucy", 5)
).toDS

assert_small_dataset_equality_error_message

The colors in the error message make it easy to identify the rows that aren't equal.

The DatasetComparer has assertSmallDatasetEquality and assertLargeDatasetEquality methods to compare either Datasets or DataFrames.

If you only need to compare DataFrames, you can use DataFrameComparer with the associated assertSmallDataFrameEquality and assertLargeDataFrameEquality methods. Under the hood, DataFrameComparer uses the assertSmallDatasetEquality and assertLargeDatasetEquality.

Setup

Option 1: Maven

Fetch the JAR file from Maven.

libraryDependencies += "com.github.mrpowers" % "spark-fast-tests_2.11" % "0.11.0" % "test"

Option 2: JitPack

Update your build.sbt file as follows.

resolvers += "jitpack" at "https://jitpack.io"
libraryDependencies += "com.github.mrpowers" % "spark-fast-tests" % "v2.3.0_0.12.0" % "test"

Why is this library fast?

The assertSmallDataFrameEquality method runs 31% faster than the assertLargeDatasetEquality method as described in this blog post.

The assertSmallDataFrameEquality method uses the Dataset collect() method, which is a lot faster than the RDD zipWithIndex() method that's used by the other Spark testing libraries (and the assertLargeDatasetEquality() method).

spark-fast-tests also provides a assertColumnEquality() method that's even faster and easier to use!

Usage

The spark-fast-tests project doesn't provide a SparkSession object in your test suite, so you'll need to make one yourself.

import org.apache.spark.sql.SparkSession

trait SparkSessionTestWrapper {

  lazy val spark: SparkSession = {
    SparkSession.builder().master("local").appName("spark session").getOrCreate()
  }

}

The DatasetComparer trait defines the assertSmallDatasetEquality method. Extend your spec file with the SparkSessionTestWrapper trait to create DataFrames and the DatasetComparer trait to make DataFrame comparisons.

import com.github.mrpowers.spark.fast.tests.DatasetComparer

class DatasetSpec extends FunSpec with SparkSessionTestWrapper with DatasetComparer {

  import spark.implicits._

    it("aliases a DataFrame") {

      val sourceDF = Seq(
        ("jose"),
        ("li"),
        ("luisa")
      ).toDF("name")

      val actualDF = sourceDF.select(col("name").alias("student"))

      val expectedDF = Seq(
        ("jose"),
        ("li"),
        ("luisa")
      ).toDF("student")

      assertSmallDatasetEquality(actualDF, expectedDF)

    }

  }

}

To compare large DataFrames that are partitioned across different nodes in a cluster, use the assertLargeDatasetEquality method.

assertLargeDatasetEquality(actualDF, expectedDF)

assertSmallDatasetEquality is faster for test suites that run on your local machine. assertLargeDatasetEquality should only be used for DataFrames that are split across nodes in a cluster.

Column Equality

The assertColumnEquality method can be used to assess the equality of two columns in a DataFrame.

Suppose you have the following DataFrame with two columns that are not equal.

+-------+-------------+
|   name|expected_name|
+-------+-------------+
|   phil|         phil|
| rashid|       rashid|
|matthew|        mateo|
|   sami|         sami|
|     li|         feng|
|   null|         null|
+-------+-------------+

The following code will throw a ColumnMismatch error message:

assertColumnEquality(df, "name", "expected_name")

assert_column_equality_error_message

Mix in the ColumnComparer trait to your test class to access the assertColumnEquality method:

import com.github.mrpowers.spark.fast.tests.ColumnComparer

object MySpecialClassTest
    extends TestSuite
    with ColumnComparer
    with SparkSessionTestWrapper {

    // your tests
}

Unordered DataFrame equality comparisons

Suppose you have the following actualDF:

+------+
|number|
+------+
|     1|
|     5|
+------+

And suppose you have the following expectedDF:

+------+
|number|
+------+
|     5|
|     1|
+------+

The DataFrames have the same columns and rows, but the order is different.

assertSmallDataFrameEquality(sourceDF, expectedDF) will throw a DatasetContentMismatch error.

We can set the orderedComparison boolean flag to false and spark-fast-tests will sort the DataFrames before performing the comparison.

assertSmallDataFrameEquality(sourceDF, expectedDF, orderedComparison = false) will not throw an error.

Equality comparisons ignoring the nullable flag

You might also want to make equality comparisons that ignore the nullable flags for the DataFrame columns.

Here is how to use the ignoreNullable flag to compare DataFrames without considering the nullable property of each column.

val sourceDF = spark.createDF(
  List(
    (1),
    (5)
  ), List(
    ("number", IntegerType, false)
  )
)

val expectedDF = spark.createDF(
  List(
    (1),
    (5)
  ), List(
    ("number", IntegerType, true)
  )
)

assertSmallDatasetEquality(sourceDF, expectedDF, ignoreNullable = true)

Testing Tips

  • Use column functions instead of UDFs as described in this blog post
  • Try to organize your code as custom transformations so it's easy to test the logic elegantly
  • Don't write tests that read from files or write files. Dependency injection is a great way to avoid file I/O in you test suite.

uTest settings to display color output

Create a CustomFramework class with overrides that turn off the default uTest color settings.

package com.github.mrpowers.spark.fast.tests

class CustomFramework extends utest.runner.Framework {
  override def formatWrapWidth: Int = 300
  // turn off the default exception message color, so spark-fast-tests
  // can send messages with custom colors
  override def exceptionMsgColor = toggledColor(utest.ufansi.Attrs.Empty)
  override def exceptionPrefixColor = toggledColor(utest.ufansi.Attrs.Empty)
  override def exceptionMethodColor = toggledColor(utest.ufansi.Attrs.Empty)
  override def exceptionPunctuationColor = toggledColor(utest.ufansi.Attrs.Empty)
  override def exceptionLineNumberColor = toggledColor(utest.ufansi.Attrs.Empty)
}

Update the build.sbt file to use the CustomFramework class:

testFrameworks += new TestFramework("com.github.mrpowers.spark.fast.tests.CustomFramework")

Alternatives

The spark-testing-base project has more features (e.g. streaming support) and is compiled to support a variety of Scala and Spark versions.

You might want to use spark-fast-tests instead of spark-testing-base in these cases:

  • You want to use uTest or a testing framework other than scalatest
  • You want to run tests in parallel (you need to set parallelExecution in Test := false with spark-testing-base)
  • You don't want to include hive as a project dependency
  • You don't want to restart the SparkSession after each test file executes so the suite runs faster

Additional Goals

  • Use memory efficiently so Spark test runs don't crash
  • Provide readable error messages
  • Easy to use in conjunction with other test suites
  • Give the user control of the SparkSession

Spark Versions

spark-fast-tests supports Spark 2.x. There are no plans to retrofit the project to work with Spark 1.x.

Publishing

Only project maintainers can publish JAR files.

For JitPack, run the scripts/multi_spark_releases.sh script to make a bunch of releases in GitHub that'll be picked up by JitPack. You need to install hub and pass in the spark-daria github_release.sh script as an argument to successfully run this command.

For Maven, follow this guide to setup your computer and then run these commands.

sbt publishSigned
sbt sonatypeRelease

Contributing

Open an issue or send a pull request to contribute. Anyone that makes good contributions to the project will be promoted to project maintainer status.