Add a script for generating test coverage reports

The script runs the unit tests via OpenCover, which also generates a
report in XML format. Then some HTML files are generated by parsing the
XML file, which are then served by `dotnet serve` tool.

The script is pretty self-explanatory. It depends on a few CLI tools:
xUnit, OpenCover (portable), codecov. These are available on Chocolatey.
It also requires a .NET Core global tool (which can be installed via
.NET Core CLI): `dotnet-reportgenerator-globaltool`. These are explained
in the script in the comments at the top.

The script is, unfortunately, for Windows only. This is due to OpenCover
being available only for Windows. I have tried some cross-platform
coverage tools (for example, @coverlet-coverage), but was not satisfied.
The problem with Coverlet is that after generating coverage for tests
covering multiple namespaces, it calculates the coverage by calculating
the simple arithmetic mean — not a weighted arithmetic mean, which would
take the number of LOC of each namespace into account.

.gitignore

@@ -1,4 +1,3 @@
-
 # Created by https://www.gitignore.io/api/linux,macos,windows,aspnetcore
 # Edit at https://www.gitignore.io/?templates=linux,macos,windows,aspnetcore
 
@@ -345,3 +344,4 @@ $RECYCLE.BIN/
 src/global.json
 tests/global.json
 .env
+report

scripts/generate-test-coverage-report.ps1

@@ -0,0 +1,23 @@
+# The following tools must be installed for this to work:
+# `xunit`, `opencover.portable`, `codecov`, and `dotnet-reportgenerator-globaltool`
+
+# These can be installed via the following commands:
+# choco install xunit opencover.portable codecov
+# dotnet tool install --global dotnet-reportgenerator-globaltool
+
+OpenCover.Console.exe `
+    -register:user `
+    -target:"C:\Program Files\dotnet\dotnet.exe" `
+    -targetargs:test `
+    -filter:"+[KonSchool*]* -[KonSchool.Tests*]*" `
+    -excludebyfile:"SchoolService.cs" `
+    -output:".\report\KonSchool_coverage.xml" `
+    -oldstyle
+
+reportgenerator -reports:.\report\KonSchool_coverage.xml -reporttypes:Html -targetdir:.\report
+dotnet serve -d .\report -p 5050
+
+# The following command opens the report in the default web browser:
+# Invoke-Expression “cmd.exe /C start http://localhost:5050"
+
+# Or, just ctrl-click on the link above 😁