fix(github-action-writer): Fix string split for property writing

src/Invex.StructuredText.GithubActions/GithubActionWriter.cs

@@ -811,7 +811,7 @@ private IDisposable WriteSection(string key, string value) =>
 
     private void WriteProperty(string key, string value)
     {
-        var lines = value.Split('\r', '\n', StringSplitOptions.RemoveEmptyEntries);
+        var lines = value.Split(['\r', '\n'], StringSplitOptions.RemoveEmptyEntries);
 
         switch (lines.Length)
         {

tests/Invex.StructuredText.GithubActions.Tests/GithubActionWriterPropertyTests.cs

@@ -0,0 +1,75 @@
+namespace Invex.StructuredText.GithubActions.Tests;
+
+/// <summary>
+///     Tests for how scalar properties are written, in particular multiline values that must be
+///     emitted as YAML block scalars. These exercise the <c>WriteProperty(string, string)</c> path
+///     via a job's <c>env</c> values.
+/// </summary>
+[TestFixture]
+internal sealed class GithubActionWriterPropertyTests
+{
+    private static string WriteEnvValue(string value)
+    {
+        var job = GithubActionWriterHelper.MinimalJob() with
+        {
+            Env = new Dictionary<string, TextExpression>
+            {
+                ["MY_VAR"] = new RawExpression(value),
+            },
+        };
+
+        return GithubActionWriterHelper.Write(GithubActionWriterHelper.MinimalAction() with
+        {
+            Jobs = [job],
+        });
+    }
+
+    [Test]
+    public void WriteProperty_ValueWithLineFeedNewlines_WritesBlockScalar()
+    {
+        var output = WriteEnvValue("line1\nline2");
+
+        output.ShouldContain("MY_VAR: |");
+        output.ShouldContain("line1");
+        output.ShouldContain("line2");
+    }
+
+    [Test]
+    public void WriteProperty_ValueWithCarriageReturnNewlines_WritesBlockScalar()
+    {
+        var output = WriteEnvValue("line1\rline2");
+
+        output.ShouldContain("MY_VAR: |");
+        output.ShouldContain("line1");
+        output.ShouldContain("line2");
+    }
+
+    [Test]
+    public void WriteProperty_ValueWithCarriageReturnLineFeedNewlines_WritesBlockScalar()
+    {
+        var output = WriteEnvValue("line1\r\nline2");
+
+        output.ShouldContain("MY_VAR: |");
+        output.ShouldContain("line1");
+        output.ShouldContain("line2");
+    }
+
+    [Test]
+    public void WriteProperty_ValueWithLineFeedNewlines_DoesNotWriteValueInline()
+    {
+        var output = WriteEnvValue("line1\nline2");
+
+        // The buggy behaviour would emit "MY_VAR: line1\nline2" inline rather than a block scalar.
+        output.ShouldNotContain("MY_VAR: line1");
+    }
+
+    [Test]
+    public void WriteProperty_SingleLineValue_WritesInline()
+    {
+        var output = WriteEnvValue("hello");
+
+        output.ShouldContain("MY_VAR: hello");
+        output.ShouldNotContain("MY_VAR: |");
+    }
+}
+