Added tests for trendlines on charts

__tests__/AddTrendlinesToAChart.tests.ps1

@@ -0,0 +1,49 @@
+Describe "Test adding trendlines to charts" {
+    BeforeAll {
+        $script:data = ConvertFrom-Csv @"
+Region,Item,TotalSold
+West,screws,60
+South,lemon,48
+South,apple,71
+East,screwdriver,70
+East,kiwi,32
+West,screwdriver,1
+South,melon,21
+East,apple,79
+South,apple,68
+South,avocado,73
+"@
+
+    }
+
+    BeforeEach {
+        $xlfile = "$env:TEMP\trendLine.xlsx"
+        Remove-Item $xlfile -ErrorAction SilentlyContinue
+    }
+
+    It "Should add a linear trendline" {
+
+        $cd = New-ExcelChartDefinition -XRange Region -YRange TotalSold -ChartType ColumnClustered -ChartTrendLine Linear
+        $data | Export-Excel $xlfile -ExcelChartDefinition $cd -AutoNameRange
+
+        $excel = Open-ExcelPackage -Path $xlfile
+        $ws = $excel.Workbook.Worksheets["Sheet1"]
+
+        $ws.Drawings[0].Series.TrendLines.Type | Should Be 'Linear'
+
+        Close-ExcelPackage $excel
+    }
+
+    It "Should add a MovingAvgerage trendline" {
+
+        $cd = New-ExcelChartDefinition -XRange Region -YRange TotalSold -ChartType ColumnClustered -ChartTrendLine MovingAvgerage
+        $data | Export-Excel $xlfile -ExcelChartDefinition $cd -AutoNameRange
+
+        $excel = Open-ExcelPackage -Path $xlfile
+        $ws = $excel.Workbook.Worksheets["Sheet1"]
+
+        $ws.Drawings[0].Series.TrendLines.Type | Should Be 'MovingAvgerage'
+
+        Close-ExcelPackage $excel
+    }
+}