test: property-check table formatter alignment under unicode content

test/property/table-formatter.property.test.ts

@@ -0,0 +1,125 @@
+import { describe, expect, it } from "vitest";
+import * as fc from "fast-check";
+import {
+	buildTable,
+	buildTableRow,
+	type TableColumn,
+	type TableOptions,
+} from "../../lib/table-formatter.js";
+import { displayWidth } from "../../lib/ui/display-width.js";
+
+// Mix single-column ASCII with double-column CJK and emoji so padding and
+// truncation are exercised in display columns, not UTF-16 code units (ui-02).
+const arbCellText = fc
+	.array(fc.constantFrom("a", "B", "7", " ", "-", "é", "漢", "字", "🚀", "⚡"), {
+		minLength: 0,
+		maxLength: 12,
+	})
+	.map((chars) => chars.join(""));
+
+const arbColumn: fc.Arbitrary<TableColumn> = fc.record({
+	header: arbCellText,
+	width: fc.integer({ min: 0, max: 10 }),
+	// undefined exercises formatCell's default-left branch.
+	align: fc.option(fc.constantFrom<"left" | "right">("left", "right"), {
+		nil: undefined,
+	}),
+});
+
+const arbOptions: fc.Arbitrary<TableOptions> = fc
+	.array(arbColumn, { minLength: 1, maxLength: 5 })
+	.map((columns) => ({ columns }));
+
+function expectedLineWidth(options: TableOptions): number {
+	const widths = options.columns.map((column) => Math.max(0, column.width));
+	return widths.reduce((sum, width) => sum + width, 0) + (options.columns.length - 1);
+}
+
+describe("table formatter property invariants", () => {
+	it("every line of any table has the exact same display width as the layout", () => {
+		fc.assert(
+			fc.property(
+				arbOptions,
+				fc.array(fc.array(arbCellText, { minLength: 0, maxLength: 6 }), {
+					minLength: 0,
+					maxLength: 8,
+				}),
+				(options, rows) => {
+					const lines = buildTable(rows, options);
+					expect(lines).toHaveLength(rows.length + 2);
+					const layoutWidth = expectedLineWidth(options);
+					for (const line of lines) {
+						// Header, separator, and every data row stay in lockstep no
+						// matter what content (incl. CJK/emoji, missing cells, or
+						// extra cells beyond the column count) lands in the rows.
+						expect(displayWidth(line)).toBe(layoutWidth);
+					}
+				},
+			),
+		);
+	});
+
+	it("content that fits is preserved verbatim with padding on the declared side", () => {
+		fc.assert(
+			fc.property(
+				arbCellText,
+				fc.integer({ min: 1, max: 14 }),
+				fc.option(fc.constantFrom<"left" | "right">("left", "right"), {
+					nil: undefined,
+				}),
+				(value, width, align) => {
+					fc.pre(displayWidth(value) <= width);
+					const row = buildTableRow([value], {
+						columns: [{ header: "h", width, align }],
+					});
+					const pad = " ".repeat(width - displayWidth(value));
+					// undefined align defaults to left.
+					expect(row).toBe(align === "right" ? pad + value : value + pad);
+				},
+			),
+		);
+	});
+
+	it("content that overflows is truncated to a prefix plus ellipsis, never overflowing", () => {
+		fc.assert(
+			fc.property(
+				arbCellText,
+				fc.integer({ min: 1, max: 6 }),
+				fc.constantFrom<"left" | "right">("left", "right"),
+				(value, width, align) => {
+					fc.pre(displayWidth(value) > width);
+					const row = buildTableRow([value], {
+						columns: [{ header: "h", width, align }],
+					});
+					expect(displayWidth(row)).toBe(width);
+					// The ellipsis terminates the visible content for either
+					// alignment (content can never follow it, so trimming trailing
+					// padding cannot eat content).
+					expect(row.trimEnd().endsWith("…")).toBe(true);
+					// Prefix fidelity is validated on the LEFT-aligned rendering,
+					// where the cell starts at column 0: stripping leading spaces on
+					// a right-aligned row could eat spaces that belong to the
+					// truncated content itself, not just alignment padding.
+					const leftRow = buildTableRow([value], {
+						columns: [{ header: "h", width, align: "left" }],
+					});
+					const visible = leftRow.replace(/ +$/, "");
+					expect(visible.endsWith("…")).toBe(true);
+					expect(value.startsWith(visible.slice(0, -1))).toBe(true);
+					expect(displayWidth(visible)).toBeLessThanOrEqual(width);
+				},
+			),
+		);
+	});
+
+	it("zero-width columns render empty and never leak an ellipsis into the layout", () => {
+		fc.assert(
+			fc.property(arbCellText, (value) => {
+				const row = buildTableRow([value], {
+					columns: [{ header: "h", width: 0 }],
+				});
+				expect(row).toBe("");
+			}),
+		);
+	});
+});