Check that the variable is not already defined

1 files changed, 16 insertions, 0 deletions

diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerContextTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerContextTests.java
index f8529083..2be22340 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerContextTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerContextTests.java
@@ -3,6 +3,7 @@ package org.shedlang.compiler.typechecker;
 import org.junit.jupiter.api.Test;
 import org.shedlang.compiler.sources.Sources;
 import org.shedlang.compiler.typechecker.errors.UnknownVariableError;
+import org.shedlang.compiler.typechecker.errors.VariableIsAlreadyDefinedError;
 import org.shedlang.compiler.types.Types;
 import org.shedlang.compiler.util.P;
 
@@ -42,4 +43,19 @@ public class TypeCheckerContextTests {
 
         assertThat(error.variableName(), equalTo("x"));
     }
+
+    @Test
+    public void givenVariableIsDefinedWhenVariableIsDefinedThenErrorIsThrown() {
+        var context = TypeCheckerContext.EMPTY
+            .enterNamespace(P.map(
+                Map.entry("x", TypeCheckerContext.defined(Types.STRING))
+            ));
+
+        var error = assertThrows(
+            VariableIsAlreadyDefinedError.class,
+            () -> context.define("x", Types.STRING, Sources.NULL)
+        );
+
+        assertThat(error.variableName(), equalTo("x"));
+    }
 }