Add option to pad ratchet percentages (#28)

src/index.ts

@@ -50,7 +50,7 @@ function onRunComplete(globalConfig: Config, options: RatchetOptions) {
       const coverageRaw = readFileSync(coverageSummaryPath, 'utf-8');
       const summary: IstanbulCoverage = JSON.parse(coverageRaw);
       const threshold = globalConfig.coverageThreshold!;
-      const ratchetResult = ratchetCoverage(threshold, summary);
+      const ratchetResult = ratchetCoverage(threshold, summary, options);
 
       updateFile(jestConfigPath, ratchetResult);
     });

src/interfaces.ts

@@ -33,8 +33,8 @@ export interface JestCoverageCategory {
 }
 
 export interface RatchetOptions {
-  disable?: boolean;
-  stop?: JestCoverage;
+  /** Pad the ratchet percentage by a specified number. */
+  ratchetPercentagePadding?: number;
 }
 
 export interface Config {

src/ratchet.ts

@@ -4,40 +4,49 @@ import {
   IstanbulCoverageCategory,
   JestCoverage,
   JestCoverageCategory,
+  RatchetOptions,
 } from './interfaces';
 
 export function ratchetCoverage(
   threshold: JestCoverage,
   summary: IstanbulCoverage,
+  options: RatchetOptions,
 ): JestCoverage {
   const result: any = {};
   for (const key of Object.keys(threshold)) {
     const summaryKey = key === 'global' ? 'total' : key;
-    result[key] = ratchetSingleCoverage(threshold[key], summary[summaryKey]);
+    result[key] = ratchetSingleCoverage(threshold[key], summary[summaryKey], options);
   }
   return result;
 }
 
 function ratchetSingleCoverage(
   threshold: JestCoverageCategory,
   summary: IstanbulCoverageCategories,
+  options: RatchetOptions,
 ) {
   const { branches, functions, lines, statements } = threshold;
   return {
-    branches: ratchetSingleNumberCoverage(branches, summary.branches),
-    functions: ratchetSingleNumberCoverage(functions, summary.functions),
-    lines: ratchetSingleNumberCoverage(lines, summary.lines),
-    statements: ratchetSingleNumberCoverage(statements, summary.statements),
+    branches: ratchetSingleNumberCoverage(branches, summary.branches, options),
+    functions: ratchetSingleNumberCoverage(functions, summary.functions, options),
+    lines: ratchetSingleNumberCoverage(lines, summary.lines, options),
+    statements: ratchetSingleNumberCoverage(statements, summary.statements, options),
   };
 }
 
 function ratchetSingleNumberCoverage(
   num: number | undefined,
   category: IstanbulCoverageCategory,
+  options: RatchetOptions,
 ) {
-  if (num && category && num > 0 && num <= category.pct) {
-    return category.pct;
-  } else if (num && category && num < 0 && num >= -category.covered) {
-    return -category.covered;
+  if (num && category) {
+    const ratchetPct = options.ratchetPercentagePadding
+      ? Math.round(category.pct) - options.ratchetPercentagePadding
+      : category.pct;
+    if (num > 0 && num <= ratchetPct) {
+      return ratchetPct;
+    } else if (num < 0 && num >= -category.covered) {
+      return -category.covered;
+    }
   }
 }

src/test.ts

@@ -114,6 +114,49 @@ describe('jest-ratchet', () => {
         }));
   });
 
+  it('will pad the ratchet percentages', () => {
+    const PADDING = 2;
+    const threshold = {
+      coverageThreshold: {
+        global: {
+          branches: 50,
+        },
+      },
+    };
+    fs.__addMockFile(
+      /\/coverage-summary\.json$/,
+      JSON.stringify({
+        total: {
+          branches: {pct: 100},
+        },
+      }),
+    );
+    fs.__addMockFile(
+      /\/package\.json$/,
+      JSON.stringify({ ...threshold }),
+    );
+
+    const jestRatchet = new JestRatchet({
+      ...mockConfig,
+      ...threshold,
+      rootDir: './example',
+    }, {
+      ratchetPercentagePadding: PADDING,
+    });
+    jestRatchet.onRunComplete();
+
+    const writeFileSync = fs.writeFileSync as jest.Mock;
+    expect(writeFileSync.mock.calls[0][1])
+      .toEqual(
+        JSON.stringify({
+          coverageThreshold: {
+            global: {
+              branches: 98,
+            },
+          },
+        }));
+  });
+
   it('will respect the --config flag', () => {
     process.argv = ['', '', '--config', 'jestconfig.json'];
     const threshold = {