[SPARK] Add common sql test utility methods to DeltaSQLTestUtils (d…

…elta-io#4131)

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#### Which Delta project/connector is this regarding?
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- [X] Spark
- [ ] Standalone
- [ ] Flink
- [ ] Kernel
- [ ] Other (fill in here)

## Description
Adding the most commonly used methods in testing; such as getting the
delta log, snapshot, protocol, stats, columns etc in `DeltaSQLTestUtils`
so that we don't have to keep reimplementing them over and over again
and just use this trait instead.

## How was this patch tested?
No testing required.

## Does this PR introduce _any_ user-facing changes?
No.

spark/src/test/scala-spark-master/org/apache/spark/sql/delta/DeltaVariantSuite.scala

@@ -43,11 +43,6 @@ class DeltaVariantSuite
 
   import testImplicits._
 
-  private def getProtocolForTable(table: String): Protocol = {
-    val deltaLog = DeltaLog.forTable(spark, TableIdentifier(table))
-    deltaLog.unsafeVolatileSnapshot.protocol
-  }
-
   private def assertVariantTypeTableFeatures(
       tableName: String,
       expectPreviewFeature: Boolean,

spark/src/test/scala/org/apache/spark/sql/delta/test/DeltaSQLTestUtils.scala

@@ -18,7 +18,17 @@ package org.apache.spark.sql.delta.test
 
 import java.io.File
 
+import scala.util.Random
+
+import org.apache.spark.sql.delta.{DeltaColumnMappingTestUtilsBase, DeltaLog, DeltaTable, Snapshot, TableFeature}
+import org.apache.spark.sql.delta.actions.Protocol
+import org.apache.spark.sql.delta.stats.{DeltaStatistics, PreparedDeltaFileIndex}
+import com.fasterxml.jackson.databind.{JsonNode, ObjectMapper}
+
+import org.apache.spark.sql.{AnalysisException, DataFrame}
+import org.apache.spark.sql.catalyst.TableIdentifier
 import org.apache.spark.sql.test.SQLTestUtils
+import org.apache.spark.sql.types._
 import org.apache.spark.util.Utils
 
 trait DeltaSQLTestUtils extends SQLTestUtils {
@@ -74,4 +84,224 @@ trait DeltaSQLTestUtils extends SQLTestUtils {
       files.foreach(Utils.deleteRecursively)
     }
   }
+
+  /** Returns random alphanumberic string to be used as a unique table name. */
+  def uniqueTableName: String = Random.alphanumeric.take(10).mkString
+
+  /** Gets the latest snapshot of the table. */
+  def getSnapshot(tableName: String): Snapshot = {
+    DeltaLog.forTable(spark, TableIdentifier(tableName)).update()
+  }
+
+  /** Gets the table protocol of the latest snapshot. */
+  def getProtocolForTable(tableName: String): Protocol = {
+    getSnapshot(tableName).protocol
+  }
+  /** Gets the `StructField` of `columnPath`. */
+  final def getColumnField(schema: StructType, columnPath: Seq[String]): StructField = {
+    schema.findNestedField(columnPath, includeCollections = true).get._2
+  }
+
+  /** Gets the `StructField` of `columnName`. */
+  def getColumnField(tableName: String, columnName: String): StructField = {
+    val deltaLog = DeltaLog.forTable(spark, TableIdentifier(tableName))
+    getColumnField(deltaLog.update().schema, columnName.split("\\."))
+  }
+
+  /** Gets the `DataType` of `columnPath`. */
+  def getColumnType(schema: StructType, columnPath: Seq[String]): DataType = {
+    getColumnField(schema, columnPath).dataType
+  }
+
+  /** Gets the `DataType` of `columnName`. */
+  def getColumnType(tableName: String, columnName: String): DataType = {
+    getColumnField(tableName, columnName).dataType
+  }
+
+  /**
+   * Gets the stats fields from the AddFiles of `snapshot`. The stats are ordered by the
+   * modification time of the files they are associated with.
+   */
+  def getUnvalidatedStatsOrderByFileModTime(snapshot: Snapshot): Array[JsonNode] = {
+    snapshot.allFiles
+      .orderBy("modificationTime")
+      .collect()
+      .map(file => new ObjectMapper().readTree(file.stats))
+  }
+
+  /**
+   * Gets the stats fields from the AddFiles of `tableName`. The stats are ordered by the
+   * modification time of the files they are associated with.
+   */
+  def getUnvalidatedStatsOrderByFileModTime(tableName: String): Array[JsonNode] =
+    getUnvalidatedStatsOrderByFileModTime(getSnapshot(tableName))
+
+  /** Gets the physical column path if there is column mapping metadata in the schema. */
+  def getPhysicalColumnPath(tableSchema: StructType, columnName: String): Seq[String] = {
+    new DeltaColumnMappingTestUtilsBase {}.getPhysicalPathForStats(
+      columnName.split("\\."), tableSchema
+    ).get
+  }
+
+  /** Gets the value of a specified field from `stats` JSON node if it exists. */
+  def getStatFieldOpt(stats: JsonNode, path: Seq[String]): Option[JsonNode] =
+    path.foldLeft(Option(stats)) {
+      case (Some(node), key) if node.has(key) => Option(node.get(key))
+      case _ => None
+    }
+
+  /** Gets the min/max stats of `columnName` from `stats` if they exist. */
+  private def getMinMaxStatsOpt(
+      tableName: String,
+      stats: JsonNode,
+      columnName: String): (Option[String], Option[String]) = {
+    val columnPath = columnName.split('.')
+    val schema = getSnapshot(tableName).schema
+    val colType = getColumnType(schema, columnPath)
+    assert(colType.isInstanceOf[StringType], s"Expected StringType, got $colType")
+
+    val physicalColumnPath = getPhysicalColumnPath(schema, columnName)
+    val minStatsPath = DeltaStatistics.MIN +: physicalColumnPath
+    val maxStatsPath = DeltaStatistics.MAX +: physicalColumnPath
+    (
+      getStatFieldOpt(stats, minStatsPath).map(_.asText()),
+      getStatFieldOpt(stats, maxStatsPath).map(_.asText()))
+  }
+
+  /** Gets the min/max stats of `columnName` from `stats`. */
+  def getMinMaxStats(
+      tableName: String,
+      stats: JsonNode,
+      columnName: String): (String, String) = {
+    val (minOpt, maxOpt) = getMinMaxStatsOpt(tableName, stats, columnName)
+    (minOpt.get, maxOpt.get)
+  }
+
+  /** Verifies whether there are min/max stats of `columnName` in `stats`. */
+  def assertMinMaxStatsPresence(
+      tableName: String,
+      stats: JsonNode,
+      columnName: String,
+      expectStats: Boolean): Unit = {
+    val (minStats, maxStats) = getMinMaxStatsOpt(tableName, stats, columnName)
+    assert(minStats.isDefined === expectStats)
+    assert(maxStats.isDefined === expectStats)
+  }
+
+  /** Verifies min/max stats values of `columnName` in `stats`. */
+  def assertMinMaxStats(
+      tableName: String,
+      stats: JsonNode,
+      columnName: String,
+      expectedMin: String,
+      expectedMax: String): Unit = {
+    val (min, max) =
+      getMinMaxStats(tableName, stats, columnName)
+    assert(min === expectedMin, s"Expected $expectedMin, got $min")
+    assert(max === expectedMax, s"Expected $expectedMax, got $max")
+  }
+
+  /** Verifies minReaderVersion and minWriterVersion of the protocol. */
+  def assertProtocolVersion(
+      protocol: Protocol,
+      minReaderVersion: Int,
+      minWriterVersion: Int): Unit = {
+    assert(protocol.minReaderVersion === minReaderVersion)
+    assert(protocol.minWriterVersion === minWriterVersion)
+  }
+
+  /** Verifies column is of expected data type. */
+  def assertColumnDataType(
+      tableName: String,
+      columnName: String,
+      expectedDataType: DataType): Unit = {
+    assert(getColumnType(tableName, columnName) === expectedDataType)
+  }
+
+  /** Verifies `columnName` does not exist in `tableName`. */
+  def assertColumnNotExist(tableName: String, columnName: String): Unit = {
+    val e = intercept[AnalysisException] {
+      sql(s"SELECT $columnName FROM $tableName")
+    }
+    assert(e.getMessage.contains(s"`$columnName` cannot be resolved"))
+  }
+
+  /**
+   * Runs `select` query on `tableName` with `predicate` and verifies the number of rows returned
+   * and files read.
+   */
+  def assertSelectQueryResults(
+      tableName: String,
+      predicate: String,
+      numRows: Int,
+      numFilesRead: Int): Unit = {
+    val query = sql(s"SELECT * FROM $tableName WHERE $predicate")
+    assertSelectQueryResults(query, numRows, numFilesRead)
+  }
+
+  /**
+   * Runs `query` and verifies the number of rows returned
+   * and files read.
+   */
+  def assertSelectQueryResults(
+      query: DataFrame,
+      numRows: Int,
+      numFilesRead: Int): Unit = {
+    assert(query.count() === numRows, s"Expected $numRows rows, got ${query.count()}")
+    val filesRead = getNumReadFiles(query)
+    assert(filesRead === numFilesRead, s"Expected $numFilesRead files read, got $filesRead")
+  }
+
+  /** Returns the number of read files by the query with given query text. */
+  def getNumReadFiles(queryText: String): Int = {
+    getNumReadFiles(sql(queryText))
+  }
+
+  /** Returns the number of read files by the given data frame query. */
+  def getNumReadFiles(df: DataFrame): Int = {
+    val deltaScans = df.queryExecution.optimizedPlan.collect {
+      case DeltaTable(prepared: PreparedDeltaFileIndex) => prepared.preparedScan
+    }
+    assert(deltaScans.size == 1)
+    deltaScans.head.files.length
+  }
+
+  /** Drops `columnName` from `tableName`. */
+  def dropColumn(tableName: String, columnName: String): Unit = {
+    sql(s"ALTER TABLE $tableName DROP COLUMN $columnName")
+    assertColumnNotExist(tableName, columnName)
+  }
+
+  /** Changes `columnName` to `newType` */
+  def alterColumnType(tableName: String, columnName: String, newType: String): Unit = {
+    sql(s"ALTER TABLE $tableName ALTER COLUMN $columnName TYPE $newType")
+  }
+
+  /** Whether the table protocol supports the given table feature. */
+  def isFeatureSupported(tableName: String, tableFeature: TableFeature): Boolean = {
+    val protocol = getProtocolForTable(tableName)
+    protocol.isFeatureSupported(tableFeature)
+  }
+
+  /** Whether the table protocol supports the given table feature. */
+  def isFeatureSupported(tableName: String, featureName: String): Boolean = {
+    val protocol = getProtocolForTable(tableName)
+    protocol.readerFeatureNames.contains(featureName) ||
+      protocol.writerFeatureNames.contains(featureName)
+  }
+
+  /** Enables table feature for `tableName` and given `featureName`. */
+  def enableTableFeature(tableName: String, featureName: String): Unit = {
+    sql(s"""
+           |ALTER TABLE $tableName
+           |SET TBLPROPERTIES('delta.feature.$featureName' = 'supported')
+           |""".stripMargin)
+    assert(isFeatureSupported(tableName, featureName))
+  }
+
+  /** Drops table feature for `tableName` and `featureName`. */
+  def dropTableFeature(tableName: String, featureName: String): Unit = {
+    sql(s"ALTER TABLE $tableName DROP FEATURE `$featureName`")
+    assert(!isFeatureSupported(tableName, featureName))
+  }
 }