ARROW-83: [C++] Add basic test infrastructure for DecimalType

Author: Uwe L. Korn <uwelk@xhochy.com>

Closes #47 from xhochy/arrow-83 and squashes the following commits:

6eabd7a [Uwe L. Korn] Remove unused forward decl
e1854e9 [Uwe L. Korn] ARROW-83: [C++] Add basic test infrastructure for DecimalType

cpp/src/arrow/types/CMakeLists.txt

@@ -34,6 +34,7 @@ install(FILES
   DESTINATION include/arrow/types)
 
 
+ADD_ARROW_TEST(decimal-test)
 ADD_ARROW_TEST(list-test)
 ADD_ARROW_TEST(primitive-test)
 ADD_ARROW_TEST(string-test)

cpp/src/arrow/types/decimal-test.cc

@@ -0,0 +1,40 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include "gtest/gtest.h"
+
+#include "arrow/types/decimal.h"
+
+namespace arrow {
+
+TEST(TypesTest, TestDecimalType) {
+  DecimalType t1(8, 4);
+
+  ASSERT_EQ(t1.type, Type::DECIMAL);
+  ASSERT_EQ(t1.precision, 8);
+  ASSERT_EQ(t1.scale, 4);
+
+  ASSERT_EQ(t1.ToString(), std::string("decimal(8, 4)"));
+
+  // Test copy constructor
+  DecimalType t2 = t1;
+  ASSERT_EQ(t2.type, Type::DECIMAL);
+  ASSERT_EQ(t2.precision, 8);
+  ASSERT_EQ(t2.scale, 4);
+}
+
+} // namespace arrow