1 files changed, 20 insertions, 0 deletions
diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerValTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerValTests.java
index 7967e442..f09c73e9 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerValTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerValTests.java
@@ -3,6 +3,7 @@ package org.shedlang.compiler.typechecker;
 import org.junit.jupiter.api.Test;
 import org.shedlang.compiler.ast.untyped.Untyped;
 import org.shedlang.compiler.ast.untyped.UntypedFunctionDefinitionNode;
+import org.shedlang.compiler.typechecker.errors.DuplicateVariableName;
 import org.shedlang.compiler.typechecker.errors.ReferenceBeforeDefinitionError;
 import org.shedlang.compiler.types.Types;
 import org.shedlang.compiler.util.P;
@@ -88,4 +89,23 @@ public class TypeCheckerValTests {
 
         assertThat(error.variableName(), equalTo("x"));
     }
+
+    @Test
+    public void duplicateVariableNamesAreNotAllowed() {
+        var untyped = UntypedFunctionDefinitionNode.builder()
+            .addStatement(Untyped.val(Untyped.targetVariable("x"), Untyped.stringLiteral("hello")))
+            .addStatement(Untyped.val(Untyped.targetVariable("x"), Untyped.stringLiteral("hello")))
+            .build();
+        var context = TypeCheckerContext.EMPTY
+            .enterBlockWithDefinedVariables(P.map(
+                Map.entry("Unit", Types.metaType(Types.UNIT))
+            ));
+
+        var error = assertThrows(
+            DuplicateVariableName.class,
+            () -> TypeChecker.typeCheckNamespaceStatement(untyped, context)
+        );
+
+        assertThat(error.variableName(), equalTo("x"));
+    }
 }