test: pin dense output around a negative operand

Add an exact-output assertion for the default dialect so the regression
also proves the left side still denses ("a- -b" / "1- -1"), not just that
no "--" forms. Kept the shared cross-dialect check invariant-only since
dialects with dashed identifiers (e.g. BigQuery) keep the "-" spaced.

Author: sarathfrancis90

test/sqlFormatter.test.ts

@@ -83,6 +83,19 @@ describe('sqlFormatter', () => {
     }).toThrow('commaPosition config is no more supported.');
   });
 
+  it('keeps the boundary space before a negative operand but stays dense elsewhere', () => {
+    // The "--" that "a - -b" would dense into re-parses as a line comment, so that
+    // one boundary keeps its space; everything else still denses ("a-" / "1-").
+    expect(format('SELECT a - -b', { denseOperators: true })).toBe(dedent`
+      SELECT
+        a- -b
+    `);
+    expect(format('SELECT 1 - -1', { denseOperators: true })).toBe(dedent`
+      SELECT
+        1- -1
+    `);
+  });
+
   describe('formatDialect()', () => {
     it('allows passing Dialect config object as a dialect parameter', () => {
       expect(formatDialect('SELECT [foo], `bar`;', { dialect: sqlite })).toBe(dedent`