add unit error message special case for operands that serialize to sa…

…me value (#954)

ark/schema/roots/unit.ts

@@ -48,7 +48,9 @@ export const unitImplementation: nodeImplementationOf<UnitDeclaration> =
 		},
 		normalize: schema => schema,
 		defaults: {
-			description: node => printable(node.unit)
+			description: node => printable(node.unit),
+			problem: ({ expected, actual }) =>
+				`${expected === actual ? `must be reference equal to ${expected} (serialized to the same value)` : `must be ${expected} (was ${actual})`}`
 		},
 		intersections: {
 			unit: (l, r) => Disjoint.from("unit", l, r),

ark/type/__tests__/objectLiteral.test.ts

@@ -54,6 +54,13 @@ contextualize(
 			})
 		})
 
+		it("serializes to same value but not reference equal", () => {
+			const t = type("===", {})
+			attest(t({}).toString()).snap(
+				"must be reference equal to {} (serialized to the same value)"
+			)
+		})
+
 		it("error in obj that has tuple that writes error at proper path", () => {
 			// @ts-expect-error
 			attest(() => type({ "a?": ["string", ["stringx", "?"]] }))