Added test for MapArray (#942)

tests/it/array/map/mod.rs

@@ -0,0 +1,51 @@
+use std::sync::Arc;
+
+use arrow2::{
+    array::*,
+    datatypes::{DataType, Field},
+};
+
+#[test]
+fn basics() {
+    let dt = DataType::Struct(vec![
+        Field::new("a", DataType::Utf8, true),
+        Field::new("b", DataType::Utf8, true),
+    ]);
+    let data_type = DataType::Map(Box::new(Field::new("a", dt.clone(), true)), false);
+
+    let field = StructArray::new(
+        dt.clone(),
+        vec![
+            Arc::new(Utf8Array::<i32>::from_slice(["a", "aa", "aaa"])) as _,
+            Arc::new(Utf8Array::<i32>::from_slice(["b", "bb", "bbb"])),
+        ],
+        None,
+    );
+
+    let array = MapArray::new(data_type, vec![0, 1, 2].into(), Arc::new(field), None);
+
+    assert_eq!(
+        array.value(0),
+        Box::new(StructArray::new(
+            dt.clone(),
+            vec![
+                Arc::new(Utf8Array::<i32>::from_slice(["a"])) as _,
+                Arc::new(Utf8Array::<i32>::from_slice(["b"])),
+            ],
+            None,
+        )) as Box<dyn Array>
+    );
+
+    let sliced = array.slice(1, 1);
+    assert_eq!(
+        sliced.value(0),
+        Box::new(StructArray::new(
+            dt,
+            vec![
+                Arc::new(Utf8Array::<i32>::from_slice(["aa"])) as _,
+                Arc::new(Utf8Array::<i32>::from_slice(["bb"])),
+            ],
+            None,
+        )) as Box<dyn Array>
+    );
+}

tests/it/array/mod.rs

@@ -6,6 +6,7 @@ mod fixed_size_binary;
 mod fixed_size_list;
 mod growable;
 mod list;
+mod map;
 mod ord;
 mod primitive;
 mod struct_;