1 files changed, 95 insertions, 0 deletions
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/CodeWriterTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/CodeWriterTests.java
new file mode 100644
index 0000000..b0ff40c
--- /dev/null
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/output/lang/CodeWriterTests.java
@@ -0,0 +1,95 @@
+package org.zwobble.hobgoblin.compiler.output.lang;
+
+import org.junit.jupiter.api.Test;
+import org.zwobble.hobgoblin.compiler.output.CodeWriter;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.util.Optional;
+
+import static org.zwobble.precisely.AssertThat.assertThat;
+import static org.zwobble.precisely.Matchers.equalTo;
+
+public class CodeWriterTests {
+    @Test
+    public void whenFileDoesNotExistThenCustomAreasAreEmpty() throws IOException {
+        var stringWriter = new StringWriter();
+        var codeWriter = CodeWriter.file(
+            new CodeWriter.InMemoryCodeWriterFile(Optional.empty(), stringWriter),
+            "//"
+        );
+
+        codeWriter.writeHeader();
+        codeWriter.write("Before");
+        codeWriter.newLine();
+        codeWriter.writeCustomArea("body");
+        codeWriter.write("After");
+        codeWriter.newLine();
+
+        assertThat(stringWriter.toString(), equalTo("""
+            // Generated by hobgoblin.
+            
+            Before
+            // Custom area start: body
+            // Custom area end: body
+            After
+            """));
+    }
+
+    @Test
+    public void whenExistingFileIsMissingCustomAreaThenCustomAreaIsEmpty() throws IOException {
+        var stringWriter = new StringWriter();
+        var codeWriter = CodeWriter.file(
+            new CodeWriter.InMemoryCodeWriterFile(Optional.of(""), stringWriter),
+            "//"
+        );
+
+        codeWriter.writeHeader();
+        codeWriter.write("Before");
+        codeWriter.newLine();
+        codeWriter.writeCustomArea("body");
+        codeWriter.write("After");
+        codeWriter.newLine();
+
+        assertThat(stringWriter.toString(), equalTo("""
+            // Generated by hobgoblin.
+            
+            Before
+            // Custom area start: body
+            // Custom area end: body
+            After
+            """));
+    }
+
+    @Test
+    public void whenExistingFileHasCustomAreasThenCustomAreaContentsArePreserved() throws IOException {
+        var stringWriter = new StringWriter();
+        var originalContents = """
+            // Custom area start: head
+            Custom head.
+            // Custom area end: head
+            // Custom area start: body
+            Custom body.
+            // Custom area end: body
+            """;
+        var codeWriter = CodeWriter.file(
+            new CodeWriter.InMemoryCodeWriterFile(Optional.of(originalContents), stringWriter),
+            "//"
+        );
+
+        codeWriter.writeHeader();
+        codeWriter.writeCustomArea("head");
+        codeWriter.writeCustomArea("body");
+
+        assertThat(stringWriter.toString(), equalTo("""
+            // Generated by hobgoblin.
+            
+            // Custom area start: head
+            Custom head.
+            // Custom area end: head
+            // Custom area start: body
+            Custom body.
+            // Custom area end: body
+            """));
+    }
+}