Assert diff app filters to be diff value

src/main/scala/uk/co/gresearch/spark/diff/App.scala

@@ -258,6 +258,11 @@ object App {
       case Some(options) => options
       case None => sys.exit(1)
     }
+    val unknownFilters = options.filter.filter(filter => !options.diffOptions.diffValues.contains(filter))
+    if (unknownFilters.nonEmpty) {
+      throw new RuntimeException(s"Filter ${unknownFilters.mkString("'", "', '", "'")} not allowed, " +
+        s"these are the configured diff values: ${options.diffOptions.diffValues.mkString("'", "', '", "'")}")
+    }
 
     // create spark session
     val spark = SparkSession.builder()

src/test/scala/uk/co/gresearch/spark/diff/AppSuite.scala

@@ -83,4 +83,29 @@ class AppSuite extends AnyFunSuite with SparkTestSession {
       }
     }
   }
+
+  test(s"run app with unknown filter") {
+    withTempPath { path =>
+      // write left dataframe as parquet
+      val leftPath = new File(path, "left.parquet").getAbsolutePath
+      DiffSuite.left(spark).write.parquet(leftPath)
+
+      // write right dataframe as csv
+      val rightPath = new File(path, "right.parquet").getAbsolutePath
+      DiffSuite.right(spark).write.parquet(rightPath)
+
+      // launch app
+      val outputPath = new File(path, "diff.parquet").getAbsolutePath
+      assertThrows[RuntimeException](
+        App.main(Array(
+          "--format", "parquet",
+          "--id", "id",
+          "--filter", "A",
+          leftPath,
+          rightPath,
+          outputPath
+        ))
+      )
+    }
+  }
 }