[MINOR][CONNECT][PYTHON] Miscellaneous cleanup in Spark Connect compo…

…nenet

### What changes were proposed in this pull request?

This PR proposes:
1. Fix the code style in `SparkConnectPlugin.scala` and `SparkBuild.scala` to be consistent with others.
2. Rename `data_frame` to `dataframe` to be consistent with existing PySpark codes.

This Pr is a sort of a followup of apache#37710

### Why are the changes needed?

To follow existing codebase, and style.

### Does this PR introduce _any_ user-facing change?

No, the codes are not released yet. The only notable change would be renaming `data_frame` to `dataframe` to be consistent.

### How was this patch tested?

Ci in this PR should validate the changes.

Closes apache#38121 from HyukjinKwon/minor-cleanup.

Authored-by: Hyukjin Kwon <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

connector/connect/src/main/scala/org/apache/spark/sql/connect/SparkConnectPlugin.scala

@@ -44,8 +44,8 @@ class SparkConnectPlugin extends SparkPlugin {
   override def driverPlugin(): DriverPlugin = new DriverPlugin {
 
     override def init(
-                       sc: SparkContext,
-                       pluginContext: PluginContext): util.Map[String, String] = {
+        sc: SparkContext,
+        pluginContext: PluginContext): util.Map[String, String] = {
       SparkConnectService.start()
       Map.empty[String, String].asJava
     }

project/SparkBuild.scala

@@ -624,25 +624,25 @@ object SparkConnect {
     // For some reason the resolution from the imported Maven build does not work for some
     // of these dependendencies that we need to shade later on.
     libraryDependencies ++= Seq(
-      "io.grpc"             % "protoc-gen-grpc-java" % BuildCommons.gprcVersion asProtocPlugin(),
-      "org.scala-lang"      % "scala-library"        % "2.12.16" % "provided",
-      "com.google.guava"    % "guava"                % "31.0.1-jre",
-      "com.google.guava"    % "failureaccess"        % "1.0.1",
-      "com.google.protobuf" % "protobuf-java"        % protoVersion % "protobuf"
+      "io.grpc" % "protoc-gen-grpc-java" % BuildCommons.gprcVersion asProtocPlugin(),
+      "org.scala-lang" % "scala-library" % "2.12.16" % "provided",
+      "com.google.guava" % "guava" % "31.0.1-jre",
+      "com.google.guava" % "failureaccess" % "1.0.1",
+      "com.google.protobuf" % "protobuf-java" % protoVersion % "protobuf"
     ),
 
     dependencyOverrides ++= Seq(
-      "com.google.guava"    % "guava"                % "31.0.1-jre",
-      "com.google.guava"    % "failureaccess"        % "1.0.1",
-      "com.google.protobuf" % "protobuf-java"        % protoVersion
+      "com.google.guava" % "guava" % "31.0.1-jre",
+      "com.google.guava" % "failureaccess" % "1.0.1",
+      "com.google.protobuf" % "protobuf-java" % protoVersion
     ),
 
     (Compile / PB.targets) := Seq(
       PB.gens.java                -> (Compile / sourceManaged).value,
       PB.gens.plugin("grpc-java") -> (Compile / sourceManaged).value
     ),
 
-    (assembly / test) := false,
+    (assembly / test) := { },
 
     (assembly / logLevel) := Level.Info,
 
@@ -1195,7 +1195,7 @@ object CopyDependencies {
       // For the SparkConnect build, we manually call the assembly target to
       // produce the shaded Jar which happens automatically in the case of Maven.
       // Later, when the dependencies are copied, we manually copy the shaded Jar only.
-      val fid = (LocalProject("connect")/assembly).value
+      val fid = (LocalProject("connect") / assembly).value
 
       (Compile / dependencyClasspath).value.map(_.data)
         .filter { jar => jar.isFile() }

python/pyspark/sql/connect/__init__.py

@@ -19,4 +19,4 @@
 Spark through this API are can be changed at any time without warning."""
 
 
-from pyspark.sql.connect.data_frame import DataFrame  # noqa: F401
+from pyspark.sql.connect.dataframe import DataFrame  # noqa: F401

python/pyspark/sql/connect/client.py

@@ -30,7 +30,7 @@
 import pyspark.sql.connect.proto.base_pb2_grpc as grpc_lib
 import pyspark.sql.types
 from pyspark import cloudpickle
-from pyspark.sql.connect.data_frame import DataFrame
+from pyspark.sql.connect.dataframe import DataFrame
 from pyspark.sql.connect.readwriter import DataFrameReader
 from pyspark.sql.connect.plan import SQL
 

python/pyspark/sql/connect/readwriter.py

@@ -15,7 +15,7 @@
 # limitations under the License.
 #
 
-from pyspark.sql.connect.data_frame import DataFrame
+from pyspark.sql.connect.dataframe import DataFrame
 from pyspark.sql.connect.plan import Read
 
 from typing import TYPE_CHECKING