feat: show hint how many lines to cover to reach threshold (#44)

Author: bartveneman

src/cli/reporters/pretty.test.ts

@@ -164,15 +164,23 @@ test.describe('only --min-line-coverage', () => {
 
 	test('failure', () => {
 		const report = {
-			...context_empty,
+			context: {
+				coverage: {
+					total_lines: 10_000,
+					covered_lines: 5022,
+				} as CoverageResult,
+			},
 			report: {
 				ok: false,
 				...min_line_coverage_failure,
 				...min_file_line_coverage_unset,
 			},
 		} satisfies Report
 		let result = print(report, show_none, dependencies)
-		expect(result).toEqual(['Failed: line coverage is 50.22%% which is lower than the threshold of 1'])
+		expect(result).toEqual([
+			'Failed: line coverage is 50.22%% which is lower than the threshold of 1',
+			'Tip: cover 4978 more lines to meet the threshold of 100%',
+		])
 	})
 })
 

src/cli/reporters/pretty.ts

@@ -29,10 +29,15 @@ export function print_lines({ report, context }: Report, params: CliArguments, {
 	if (report.min_line_coverage.ok) {
 		output.push(`${styleText(['bold', 'green'], 'Success')}: total line coverage is ${percentage(report.min_line_coverage.actual)}`)
 	} else {
+		let { actual, expected } = report.min_line_coverage
 		output.push(
-			`${styleText(['bold', 'red'], 'Failed')}: line coverage is ${percentage(
-				report.min_line_coverage.actual,
-			)}% which is lower than the threshold of ${report.min_line_coverage.expected}`,
+			`${styleText(['bold', 'red'], 'Failed')}: line coverage is ${percentage(actual)}% which is lower than the threshold of ${expected}`,
+		)
+		let lines_to_cover = expected * context.coverage.total_lines - context.coverage.covered_lines
+		output.push(
+			`Tip: cover ${Math.ceil(lines_to_cover)} more ${lines_to_cover === 1 ? 'line' : 'lines'} to meet the threshold of ${percentage(
+				expected,
+			)}`,
 		)
 	}
 
@@ -60,6 +65,9 @@ export function print_lines({ report, context }: Report, params: CliArguments, {
 		print_width = print_width ?? 80
 		let min_file_line_coverage = report.min_file_line_coverage.expected
 
+		// Show empty line between report header and chunks output
+		output.push()
+
 		for (let sheet of context.coverage.coverage_per_stylesheet.sort((a, b) => a.line_coverage_ratio - b.line_coverage_ratio)) {
 			if (
 				(sheet.line_coverage_ratio !== 1 && params['show-uncovered'] === 'all') ||