2. Build and test .NET and Java

The project

code/github-actions holds the same small function twice — turn a title into a URL slug — with four tests on each side:

	.NET	Java
Code	dotnet/Slugs/Slug.cs	java/src/main/java/com/example/slugs/Slug.java
Tests	xUnit v3 [Theory] + [InlineData]	JUnit 6 @ParameterizedTest + @CsvSource
Command	dotnet test	mvn -B verify
SDK pinned by	global.json	maven.compiler.release in pom.xml

From dotnet/Slugs.Tests/SlugTests.cs, lines 8-14:

[Theory]
[InlineData("Hello, Wörld!", "hello-world")]
[InlineData("  GitHub   Actions  ", "github-actions")]
[InlineData("C# 14 & .NET 10", "c-14-net-10")]
[InlineData("", "")]
public void From_builds_a_lowercase_ascii_slug(string text, string expected) =>
    Assert.Equal(expected, Slug.From(text));

Before any YAML: it must pass locally, with the same commands CI will run. That’s where the first two traps of this lesson appeared.

Trap 1: xUnit v3 and dotnet test on the .NET 10 SDK

With xunit.v3 4.0.1, the first dotnet test failed before running anything:

error : Testing with VSTest target is no longer supported by Microsoft.Testing.Platform on .NET 10 SDK and later. If you use dotnet test, you should opt-in to the new dotnet test experience. For more information, see https://aka.ms/dotnet-test-mtp-error

xUnit v3 runs on Microsoft.Testing.Platform, and the .NET 10 SDK wants you to opt in to the new dotnet test explicitly, in global.json (dotnet/global.json):

{
  "sdk": {
    "version": "10.0.100",
    "rollForward": "latestFeature"
  },
  "test": {
    "runner": "Microsoft.Testing.Platform"
  }
}

Trap 2: no implicit using Xunit

Next error:

CS0246: The type or namespace name 'Theory' could not be found (are you missing a using directive or an assembly reference?)
CS0246: The type or namespace name 'InlineData' could not be found (are you missing a using directive or an assembly reference?)

With ImplicitUsings enabled, this 4.0.1 package didn’t add Xunit to the global usings: the test file needs using Xunit;. Then:

Test run summary: Passed!
  total: 4
  failed: 0
  succeeded: 4
  skipped: 0

The workflow

.github/workflows/gha-02-build.yml:

# GitHub Actions course, lesson 2: build and test .NET and Java on three OSes
name: "GHA 02: build and test"

on:
  workflow_dispatch:
  push:
    branches: [main]
    paths: ['code/github-actions/**', '.github/workflows/gha-02-build.yml']
  pull_request:
    paths: ['code/github-actions/**', '.github/workflows/gha-02-build.yml']

jobs:
  dotnet:
    name: dotnet (${{ matrix.os }})
    strategy:
      fail-fast: false
      matrix:
        os: [ubuntu-latest, windows-latest, macos-latest]
    runs-on: ${{ matrix.os }}
    defaults:
      run:
        working-directory: code/github-actions/dotnet
    steps:
      - uses: actions/checkout@v7
      - uses: actions/setup-dotnet@v6
        with:
          global-json-file: code/github-actions/dotnet/global.json
      - run: dotnet --version
      - run: dotnet test

  java:
    name: java (${{ matrix.os }})
    strategy:
      fail-fast: false
      matrix:
        os: [ubuntu-latest, windows-latest, macos-latest]
    runs-on: ${{ matrix.os }}
    defaults:
      run:
        working-directory: code/github-actions/java
    steps:
      - uses: actions/checkout@v7
      - uses: actions/setup-java@v6
        with:
          distribution: temurin
          java-version: '25'
          cache: maven
      - run: java --version
      - run: mvn -B verify

Element	Effect
strategy.matrix.os	one job per value: 3 dotnet jobs and 3 java jobs, all in parallel
fail-fast: false	a failure on Windows doesn’t cancel the macOS job still running (the default, true, does)
name: dotnet (${{ matrix.os }})	the job name shown in the run; without name, GitHub uses the job id and all matrix values, e.g. java (ubuntu-latest, 22)
defaults.run.working-directory	every run: starts in that folder (uses: steps aren’t affected)
actions/setup-dotnet with global-json-file	installs the SDK that global.json asks for
actions/setup-java with cache: maven	installs Temurin 25 and caches ~/.m2/repository, keyed on the hash of pom.xml
mvn -B	batch mode: no colors, no download progress bars in the log

What the run shows

All six jobs passed. Excerpts:

dotnet (ubuntu-latest) | dotnet-install: Installed version is 10.0.401
dotnet (ubuntu-latest) | 10.0.401
java (ubuntu-latest)   | Resolved Java 25.0.4+1 from tool-cache
java (ubuntu-latest)   | openjdk 25.0.4.1 2026-08-18 LTS
java (ubuntu-latest)   | [INFO] Tests run: 4, Failures: 0, Errors: 0, Skipped: 0
java (ubuntu-latest)   | [INFO] BUILD SUCCESS

• global.json says 10.0.100 with rollForward: latestFeature: setup-dotnet installed the latest 10.0 feature band, 10.0.401. Pin "rollForward": "disable" if you need exactly one SDK.
• Temurin 25 was already in the Ubuntu image (from tool-cache): no download.

The shell isn’t the same everywhere. The same run: dotnet test step logged:

dotnet (ubuntu-latest)  | shell: /usr/bin/bash -e {0}
dotnet (macos-latest)   | shell: /bin/bash -e {0}
dotnet (windows-latest) | shell: C:\Program Files\PowerShell\7\pwsh.EXE -command ". '{0}'"

On Windows, run: defaults to PowerShell 7. dotnet test and mvn -B verify behave the same in both, but a script with $(pwd), export or && chains won’t. Set defaults.run.shell: bash for the job (Git Bash is installed on Windows runners) when a script must be identical on the three OSes.

The cache, measured

The first run found no Maven cache and saved one; a second run (started with gh workflow run gha-02-build.yml) restored it (setup-java/src/cache.ts):

maven cache is not found
Cache saved with the key: setup-java-Linux-x64-maven-4b450ab7781caaed20d3b55ef20c4500aaacb6aad3f54b145929988a7515a1eb

Cache restored from key: setup-java-Linux-x64-maven-4b450ab7781caaed20d3b55ef20c4500aaacb6aad3f54b145929988a7515a1eb
Cache hit occurred on the primary key setup-java-Linux-x64-maven-4b450ab7781caaed20d3b55ef20c4500aaacb6aad3f54b145929988a7515a1eb, not saving cache.

Job	1st run (no cache)	2nd run (cache hit)
java (ubuntu-latest)	16 s	10 s
java (windows-latest)	43 s	28 s
java (macos-latest)	20 s	9 s
dotnet (ubuntu-latest)	21 s	22 s
dotnet (windows-latest)	60 s	57 s
dotnet (macos-latest)	20 s	22 s

The .NET jobs didn’t get faster: nothing caches the NuGet packages yet. setup-dotnet has a cache: true option based on packages.lock.json files, measured in lesson 5. The key contains the OS (Linux-x64, Windows-x64, macOS-arm64): each OS has its own cache. And macos-latest is an arm64 machine.

Key takeaways

• Make it pass locally first, with exactly the commands CI runs.
• A matrix multiplies a job; fail-fast: false lets every combination finish.
• setup-dotnet reads global.json; setup-java installs a JDK and caches Maven or Gradle.
• run: is bash on Linux/macOS and PowerShell 7 on Windows unless you set shell.
• Measure: a Maven cache hit saved 6 to 15 seconds per job here; Windows jobs are the slowest.

Exercises

1. Add 22 next to 25 so that the Java job also runs on Java 22, on the three OSes. How many Java jobs will run?

Solution

    name: java ${{ matrix.java }} (${{ matrix.os }})
    strategy:
      fail-fast: false
      matrix:
        os: [ubuntu-latest, windows-latest, macos-latest]
        java: ['25', '22']
    steps:
      - uses: actions/setup-java@v6
        with:
          distribution: temurin
          java-version: ${{ matrix.java }}
          cache: maven

6 jobs (3 × 2). But the build fails on 22: pom.xml sets maven.compiler.release to 25. Checked with gha-02-exercises.yml:

[INFO] BUILD FAILURE
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.15.0:compile (default-compile) on project slugs: Fatal error compiling: error: release version 25 not supported -> [Help 1]

A matrix tests combinations; the project must support them.

2. You want the Windows job to run dotnet test in bash, like the others. Where do you put shell: bash, so that it applies to every run: of the job?

Solution

    defaults:
      run:
        shell: bash
        working-directory: code/github-actions/dotnet

defaults.run at the job level (or at the workflow level for all jobs). On Windows the log then shows:

shell: C:\Program Files\Git\bin\bash.EXE --noprofile --norc -e -o pipefail {0}
bash 5.3.15(2)-release, options ehB

Note -o pipefail: an explicit shell: bash also fails when a command in the middle of a pipe fails, which the implicit bash -e {0} of Linux runners doesn’t do.

3. Without using Xunit;, which error would CI show, and on how many jobs?

Solution

CS0246: The type or namespace name 'Theory' could not be found, on the three dotnet jobs. With fail-fast: false all three run to the end; with the default fail-fast: true, the first failure cancels the other dotnet jobs still in progress — the java jobs come from another job definition, with its own matrix, and aren’t affected.

Sources

• Building and testing .NET — GitHub Docs
• Building and testing Java with Maven — GitHub Docs
• Running variations of jobs in a workflow (matrix)
• Testing with dotnet test and Microsoft.Testing.Platform
• global.json overview