Add summary badge to report

__tests__/__outputs__/dart-json.md

@@ -1,3 +1,5 @@
+![Tests failed](https://img.shields.io/badge/tests-1%20passed%2C%201%20skipped%2C%204%20failed-critical)
+
 ### fixtures/dart-json.json
 
 **6** tests were completed in **3.760s** with **1** passed, **1** skipped and **4** failed.

__tests__/__outputs__/dotnet-trx.md

@@ -1,3 +1,5 @@
+![Tests failed](https://img.shields.io/badge/tests-3%20passed%2C%201%20skipped%2C%203%20failed-critical)
+
 ### fixtures/dotnet-trx.trx
 
 **7** tests were completed in **1.061s** with **3** passed, **1** skipped and **3** failed.

__tests__/__outputs__/jest-junit.md

@@ -1,3 +1,5 @@
+![Tests failed](https://img.shields.io/badge/tests-1%20passed%2C%201%20skipped%2C%204%20failed-critical)
+
 ### fixtures/jest-junit.xml
 
 **6** tests were completed in **1.360s** with **1** passed, **1** skipped and **4** failed.

__tests__/__snapshots__/dart-json.test.ts.snap

@@ -52,7 +52,9 @@ dart:isolate  _RawReceivePortImpl._handleMessage
       "title": "[test\\\\second_test.dart] Timeout test",
     },
   ],
-  "summary": "### fixtures/dart-json.json
+  "summary": "![Tests failed](https://img.shields.io/badge/tests-1%20passed%2C%201%20skipped%2C%204%20failed-critical)
+
+### fixtures/dart-json.json
 
 **6** tests were completed in **3.760s** with **1** passed, **1** skipped and **4** failed.
 

__tests__/__snapshots__/dotnet-trx.test.ts.snap

@@ -30,7 +30,9 @@ Actual:   2",
       "title": "[DotnetTests.XUnitTests.CalculatorTests] Failing_Test",
     },
   ],
-  "summary": "### fixtures/dotnet-trx.trx
+  "summary": "![Tests failed](https://img.shields.io/badge/tests-3%20passed%2C%201%20skipped%2C%203%20failed-critical)
+
+### fixtures/dotnet-trx.trx
 
 **7** tests were completed in **1.061s** with **3** passed, **1** skipped and **3** failed.
 

__tests__/__snapshots__/jest-junit.test.ts.snap

@@ -73,7 +73,9 @@ Received: false
       "title": "[__tests__\\\\second.test.js] Timeout test",
     },
   ],
-  "summary": "### fixtures/jest-junit.xml
+  "summary": "![Tests failed](https://img.shields.io/badge/tests-1%20passed%2C%201%20skipped%2C%204%20failed-critical)
+
+### fixtures/jest-junit.xml
 
 **6** tests were completed in **1.360s** with **1** passed, **1** skipped and **4** failed.
 

src/report/get-report.ts

@@ -4,14 +4,36 @@ import {Align, Icon, link, table} from '../utils/markdown-utils'
 import {slug} from '../utils/slugger'
 
 export default function getReport(results: TestRunResult[]): string {
+  const badge = getBadge(results)
   const runsSummary = results.map(getRunSummary).join('\n\n')
   const suites = results
     .flatMap(tr => tr.suites)
     .map((ts, i) => getSuiteSummary(ts, i))
     .join('\n')
 
   const suitesSection = `# Test Suites\n\n${suites}`
-  return [runsSummary, suitesSection].join('\n\n')
+  return [badge, runsSummary, suitesSection].join('\n\n')
+}
+
+function getBadge(results: TestRunResult[]): string {
+  const passed = results.reduce((sum, tr) => sum + tr.passed, 0)
+  const skipped = results.reduce((sum, tr) => sum + tr.skipped, 0)
+  const failed = results.reduce((sum, tr) => sum + tr.failed, 0)
+
+  const passedText = passed > 0 ? `${passed} passed` : null
+  const skippedText = skipped > 0 ? `${skipped} skipped` : null
+  const failedText = failed > 0 ? `${failed} failed` : null
+  const message = [passedText, skippedText, failedText].filter(s => s != null).join(', ') || 'none'
+  let color = 'success'
+  if (failed > 0) {
+    color = 'critical'
+  } else if (passed === 0 && failed === 0) {
+    color = 'yellow'
+  }
+
+  const uri = encodeURIComponent(`tests-${message}-${color}`)
+  const text = failed > 0 ? 'Tests failed' : 'Tests passed successfully'
+  return `![${text}](https://img.shields.io/badge/${uri})`
 }
 
 function getRunSummary(tr: TestRunResult): string {