Add demo unit tests to learn unit testing

src/RollABall/Assembly-CSharp.csproj

src/RollABall/Assets/Scenes/PlayModeTests/DemoTest.cs

...ollABall/Assets/Scenes/PlayModeTests/PlayModeTests.asmdef

src/RollABall/Assets/Scripts/NewMenuItem.cs

src/RollABall/Assets/Scripts/NewMenuItemTest.cs.meta

src/RollABall/Assets/UnitTests/EditMode/DemoTest.cs

src/RollABall/Assets/UnitTests/UnitTests.asmdef

src/RollABall/Library/CurrentLayout.dwlt

src/RollABall/Library/EditorInstance.json

src/RollABall/Library/LastBuild.buildreport

src/RollABall/Library/LastSceneManagerSetup.txt

...ollABall/Library/ScriptAssemblies/Assembly-CSharp.dll.mdb

src/RollABall/Library/assetDatabase3

src/RollABall/Library/expandedItems

...Ball/Library/metadata/ff/ff2f78ceaf5944fc089cc08a54c7e2c9

...Library/metadata/ff/ff2f78ceaf5944fc089cc08a54c7e2c9.info

...RollABall/Library/shadercompiler-UnityShaderCompiler0.log

src/RollABall/PlayModeTests.csproj

src/RollABall/RollABall.sln

src/RollABall/Temp/__Backupscenes/0.backup