test(language/lint): add unit tests for unused-variable pass

packages/language/src/lint/unused-variable.test.ts

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2026, Salesforce, Inc.
+ * All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ * For full license text, see the LICENSE file in the repo root or https://www.apache.org/licenses/LICENSE-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import { parse } from '@agentscript/parser';
+import { Dialect } from '../core/dialect.js';
+import { NamedBlock, NamedCollectionBlock } from '../core/block.js';
+import { ExpressionValue } from '../core/primitives.js';
+import { LintEngine } from '../core/analysis/lint-engine.js';
+import { createSchemaContext } from '../core/analysis/scope.js';
+import { VariablesBlock } from '../blocks.js';
+import { unusedVariablePass } from './unused-variable.js';
+
+const ValueBlock = NamedBlock('ValueBlock', {
+  expr: ExpressionValue.describe('An expression that may reference variables'),
+});
+
+const TestSchema = {
+  variables: VariablesBlock,
+  value: NamedCollectionBlock(ValueBlock),
+};
+
+const schemaCtx = createSchemaContext({ schema: TestSchema, aliases: {} });
+
+function getDiagnostics(source: string) {
+  const { rootNode: root } = parse(source);
+  const mappingNode =
+    root.namedChildren.find(n => n.type === 'mapping') ?? root;
+
+  const dialect = new Dialect();
+  const result = dialect.parse(mappingNode, TestSchema);
+
+  const engine = new LintEngine({
+    passes: [unusedVariablePass()],
+    source: 'test',
+  });
+  const { diagnostics } = engine.run(result.value, schemaCtx);
+  return diagnostics.filter(d => d.code === 'unused-variable');
+}
+
+describe('unused-variable lint pass', () => {
+  it('flags a variable that is declared but never referenced', () => {
+    const diags = getDiagnostics(`
+variables:
+    unused: mutable string = ""
+`);
+    expect(diags).toHaveLength(1);
+    expect(diags[0].message).toContain('unused');
+  });
+
+  it('does not flag a variable that is referenced in an expression', () => {
+    const diags = getDiagnostics(`
+variables:
+    used: mutable string = ""
+
+value v:
+    expr: @variables.used
+`);
+    expect(diags).toHaveLength(0);
+  });
+
+  it('flags only the unused variables when multiple are declared', () => {
+    const diags = getDiagnostics(`
+variables:
+    used: mutable string = ""
+    unused: mutable string = ""
+
+value v:
+    expr: @variables.used
+`);
+    expect(diags).toHaveLength(1);
+    expect(diags[0].message).toContain('unused');
+  });
+
+  it('reports one diagnostic per unused variable', () => {
+    const diags = getDiagnostics(`
+variables:
+    a: mutable string = ""
+    b: mutable string = ""
+    c: mutable string = ""
+`);
+    expect(diags).toHaveLength(3);
+  });
+
+  it('does not flag variables when no `variables:` block is declared', () => {
+    const diags = getDiagnostics(`
+value v:
+    expr: @variables.foo
+`);
+    expect(diags).toHaveLength(0);
+  });
+});