Add unit test for grid layout:

1. Pixel row column
1. Start row column
1. Mix pixel star row column

tests/Avalonia.Controls.UnitTests/Avalonia.Controls.UnitTests.csproj

@@ -3,6 +3,9 @@
     <TargetFrameworks>netcoreapp2.0</TargetFrameworks>
     <OutputType>Library</OutputType>
   </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Debug|netcoreapp2.0|AnyCPU'">
+    <LangVersion>latest</LangVersion>
+  </PropertyGroup>
   <Import Project="..\..\build\UnitTests.NetCore.targets" />
   <Import Project="..\..\build\Moq.props" />
   <Import Project="..\..\build\XUnit.props" />

tests/Avalonia.Controls.UnitTests/GridMocks.cs

@@ -0,0 +1,98 @@
+using System;
+using System.Diagnostics.CodeAnalysis;
+using Xunit;
+
+namespace Avalonia.Controls.UnitTests
+{
+    internal static class GridMock
+    {
+        /// <summary>
+        /// Create a mock grid to test its row layout.
+        /// This method contains Arrange (`new Grid()`) and Action (`Measure()`/`Arrange()`).
+        /// </summary>
+        /// <param name="rows">The row definitions of this mock grid.</param>
+        /// <param name="measure">The measure height of this grid. PositiveInfinity by default.</param>
+        /// <param name="arrange">The arrange height of this grid. DesiredSize.Height by default.</param>
+        /// <returns>The mock grid that its children bounds will be tested.</returns>
+        [SuppressMessage("ReSharper", "CompareOfFloatsByEqualityOperator")]
+        internal static Grid New(RowDefinitions rows,
+            double measure = default, double arrange = default)
+        {
+            var grid = new Grid { RowDefinitions = rows };
+            for (var i = 0; i < rows.Count; i++)
+            {
+                grid.Children.Add(new Border { [Grid.RowProperty] = i });
+            }
+
+            grid.Measure(new Size(double.PositiveInfinity, measure == default ? double.PositiveInfinity : measure));
+            grid.Arrange(new Rect(0, 0, 0, arrange == default ? grid.DesiredSize.Width : arrange));
+
+            return grid;
+        }
+
+        /// <summary>
+        /// Create a mock grid to test its column layout.
+        /// This method contains Arrange (`new Grid()`) and Action (`Measure()`/`Arrange()`).
+        /// </summary>
+        /// <param name="columns">The column definitions of this mock grid.</param>
+        /// <param name="measure">The measure width of this grid. PositiveInfinity by default.</param>
+        /// <param name="arrange">The arrange width of this grid. DesiredSize.Width by default.</param>
+        /// <returns>The mock grid that its children bounds will be tested.</returns>
+        [SuppressMessage("ReSharper", "CompareOfFloatsByEqualityOperator")]
+        internal static Grid New(ColumnDefinitions columns,
+            double measure = default, double arrange = default)
+        {
+            var grid = new Grid { ColumnDefinitions = columns };
+            for (var i = 0; i < columns.Count; i++)
+            {
+                grid.Children.Add(new Border { [Grid.ColumnProperty] = i });
+            }
+
+            grid.Measure(new Size(measure == default ? double.PositiveInfinity : measure, double.PositiveInfinity));
+            grid.Arrange(new Rect(0, 0, arrange == default ? grid.DesiredSize.Width : arrange, 0));
+
+            return grid;
+        }
+    }
+
+    internal static class GridAssert
+    {
+        /// <summary>
+        /// Assert all the children heights.
+        /// This method will assume that the grid children count equals row count.
+        /// </summary>
+        /// <param name="grid">The children will be fetched through it.</param>
+        /// <param name="rows">Expected row values of every children.</param>
+        internal static void ChildrenHeight(Grid grid, params double[] rows)
+        {
+            if (grid.Children.Count != rows.Length)
+            {
+                throw new NotSupportedException();
+            }
+
+            for (var i = 0; i < rows.Length; i++)
+            {
+                Assert.Equal(rows[i], grid.Children[i].Bounds.Height);
+            }
+        }
+
+        /// <summary>
+        /// Assert all the children widths.
+        /// This method will assume that the grid children count equals row count.
+        /// </summary>
+        /// <param name="grid">The children will be fetched through it.</param>
+        /// <param name="columns">Expected column values of every children.</param>
+        internal static void ChildrenWidth(Grid grid, params double[] columns)
+        {
+            if (grid.Children.Count != columns.Length)
+            {
+                throw new NotSupportedException();
+            }
+
+            for (var i = 0; i < columns.Length; i++)
+            {
+                Assert.Equal(columns[i], grid.Children[i].Bounds.Width);
+            }
+        }
+    }
+}

tests/Avalonia.Controls.UnitTests/GridTests.cs

@@ -1,6 +1,8 @@
 // Copyright (c) The Avalonia Project. All rights reserved.
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
+using System.Diagnostics.CodeAnalysis;
+using System.Globalization;
 using Avalonia.Controls;
 using Xunit;
 
@@ -64,5 +66,41 @@ namespace Avalonia.Controls.UnitTests
             Assert.Equal(new Rect(0, 25, 150, 25), target.Children[1].Bounds);
             Assert.Equal(new Rect(154, 25, 50, 25), target.Children[2].Bounds);
         }
+
+        [Fact]
+        public void Layout_PixelRowColumn_BoundsCorrect()
+        {
+            // Arrange & Action
+            var rowGrid = GridMock.New(new RowDefinitions("100,200,300"));
+            var columnGrid = GridMock.New(new ColumnDefinitions("50,100,150"));
+
+            // Assert
+            GridAssert.ChildrenHeight(rowGrid, 100, 200, 300);
+            GridAssert.ChildrenWidth(columnGrid, 50, 100, 150);
+        }
+
+        [Fact]
+        public void Layout_StarRowColumn_BoundsCorrect()
+        {
+            // Arrange & Action
+            var rowGrid = GridMock.New(new RowDefinitions("1*,2*,3*"), arrange: 600);
+            var columnGrid = GridMock.New(new ColumnDefinitions("*,*,2*"), arrange: 600);
+
+            // Assert
+            GridAssert.ChildrenHeight(rowGrid, 100, 200, 300);
+            GridAssert.ChildrenWidth(columnGrid, 150, 150, 300);
+        }
+
+        [Fact]
+        public void Layout_MixPixelStarRowColumn_BoundsCorrect()
+        {
+            // Arrange & Action
+            var rowGrid = GridMock.New(new RowDefinitions("1*,2*,150"), arrange: 600);
+            var columnGrid = GridMock.New(new ColumnDefinitions("1*,2*,150"), arrange: 600);
+
+            // Assert
+            GridAssert.ChildrenHeight(rowGrid, 150, 300, 150);
+            GridAssert.ChildrenWidth(columnGrid, 150, 300, 150);
+        }
     }
 }