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Apache Spark testing helpers (dependency free & works with Scalatest, uTest, and MUnit)
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spark-fast-tests

A fast Apache Spark testing helper library with beautifully formatted error messages! Works with scalatest and uTest.

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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.

Note : comparing Datasets can be tricky since some column names might be given by Spark when applying transformations. Use the ignoreColumnNames boolean to skip name verification.

Setup

Option 1: Maven

Fetch the JAR file from Maven.

resolvers += "Spark Packages Repo" at "http://dl.bintray.com/spark-packages/maven"

// Scala 2.11
libraryDependencies += "MrPowers" % "spark-fast-tests" % "0.20.0-s_2.11"

// Scala 2.12, Spark 2.4+
libraryDependencies += "MrPowers" % "spark-fast-tests" % "0.20.0-s_2.12"

Here's a link to all the JAR files in Maven.

Option 2: JitPack

Update your build.sbt file as follows.

resolvers += "jitpack" at "https://jitpack.io"
libraryDependencies += "com.github.mrpowers" % "spark-fast-tests" % "v0.16.0" % "test"

Spark version compatibility by spark-fast-tests version

0.16.0 0.17.0
2.0.0
2.1.0
2.2.2
2.3.0
2.3.1
2.4.0

Scala 2.12 support is only for Spark 2.4+.

Why is this library fast?

This library provides three main methods to test your code.

Suppose you'd like to test this function:

def myLowerClean(col: Column): Column = {
  lower(regexp_replace(col, "\\s+", ""))
}

Here's how long the tests take to execute:

test method runtime
assertLargeDataFrameEquality 709 milliseconds
assertSmallDataFrameEquality 166 milliseconds
assertColumnEquality 108 milliseconds
evalString 26 milliseconds

evalString isn't the most robust for testing, but is the fastest. assertColumnEquality is robust and we can see it saves a lot of time.

Other testing libraries don't have methods like assertSmallDataFrameEquality or assertColumnEquality so they run slower.

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")
      .config("spark.sql.shuffle.partitions", "1")
      .getOrCreate()
  }

}

It's typically best set the number of shuffle partitions to one in your test suite. This configuration can make your tests run up to 70% faster. You can remove this configuration option or adjust it if you're working with big DataFrames in your test suite.

Make sure to only use the SparkSessionTestWrapper trait in your test suite. You don't want to use test specific configuration (like one shuffle partition) when running production code.

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 org.apache.spark.sql.types._
import org.apache.spark.sql.Row
import org.apache.spark.sql.functions._
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)

Approximate DataFrame Equality

The assertApproximateDataFrameEquality function is useful for DataFrames that contain DoubleType columns. The precision threshold must be set when using the assertApproximateDataFrameEquality function.

val sourceDF = spark.createDF(
  List(
    (1.2),
    (5.1),
    (null)
  ), List(
    ("number", DoubleType, true)
  )
)

val expectedDF = spark.createDF(
  List(
    (1.2),
    (5.1),
    (null)
  ), List(
    ("number", DoubleType, true)
  )
)

assertApproximateDataFrameEquality(sourceDF, expectedDF, 0.01)

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

Publishing

Build the JAR / POM files with sbt +spDist as described in this GitHub issue.

Manually upload the zip files to Spark Packages.

Make a GitHub release so the code is available via JitPack.

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

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.

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