diff --git a/src/test/scala/GlobalStatisticsAnalysisTests.scala b/src/test/scala/GlobalStatisticsAnalysisTests.scala
new file mode 100644
index 0000000..c42d2bd
--- /dev/null
+++ b/src/test/scala/GlobalStatisticsAnalysisTests.scala
@@ -0,0 +1,50 @@
+import zio.test._
+import zio.test.Assertion._
+import zio.Chunk
+import GlobalStatisticsAnalysis._
+import java.time.LocalDate
+
+object GlobalStatsSpec extends ZIOSpecDefault {
+  def getTestPath(filename: String): String = {
+    getClass.getClassLoader.getResource(filename).getFile()
+  }
+
+  def spec: Spec[TestEnvironment, Any] = suite("GlobalStatistics")(
+    test("getFieldsStatistics should return empty list if no data in period") {
+      val data = Chunk(
+        (LocalDate.of(2021, 1, 1), 1.0f),
+        (LocalDate.of(2021, 1, 2), 2.0f)
+      )
+      val fields = List(
+        FieldSelector("fieldName", (x: (LocalDate, Float)) => x._2)
+      )
+      val start  = LocalDate.of(2022, 1, 1)
+      val end    = LocalDate.of(2022, 12, 31)
+      val result = GlobalStatisticsAnalysis.getFieldsStatistics(data, fields, (x: (LocalDate, Float)) => x._1, start, end)
+      assert(result)(equalTo(Nil))
+    },
+    test("getFieldsStatistics should return correct statistics") {
+      val data = Chunk(
+        (LocalDate.of(2021, 1, 1), 1.0f),
+        (LocalDate.of(2021, 1, 2), 2.0f)
+      )
+      val fields = List(
+        FieldSelector("fieldName", (x: (LocalDate, Float)) => x._2)
+      )
+      val start  = LocalDate.of(2021, 1, 1)
+      val end    = LocalDate.of(2021, 1, 2)
+      val result = GlobalStatisticsAnalysis.getFieldsStatistics(data, fields, (x: (LocalDate, Float)) => x._1, start, end)
+      assert(result)(equalTo(List(Statistics("fieldName", 1.5, 0.5, 1.0, 2.0, 2))))
+    },
+    test("getFieldsStatistics should return empty list if empty data") {
+      val data = Chunk.empty
+      val fields = List(
+        FieldSelector("fieldName", (x: (LocalDate, Float)) => x._2)
+      )
+      val start  = LocalDate.of(2021, 1, 1)
+      val end    = LocalDate.of(2021, 1, 2)
+      val result = GlobalStatisticsAnalysis.getFieldsStatistics(data, fields, (x: (LocalDate, Float)) => x._1, start, end)
+      assert(result)(equalTo(Nil))
+    }
+  )
+}