fix: enhance coverage reporting with handling for undefined coverageB…

…efore

__tests__/message.test.ts

@@ -16,7 +16,7 @@ describe('buildMessage', () => {
     coverage: [],
     coverageBefore: [],
     coverageFile: 'packages/project_a/coverage/lcov.info'
-  }
+  } as CoveredProject
 
   const projectB = {
     name: 'project_b',
@@ -25,7 +25,7 @@ describe('buildMessage', () => {
     coverage: [],
     coverageBefore: [],
     coverageFile: 'packages/project_b/coverage/lcov.info'
-  }
+  } as CoveredProject
 
   it('returns the correct message when projects array has one project', () => {
     const projects: CoveredProject[] = [projectA]
@@ -40,6 +40,16 @@ describe('buildMessage', () => {
     const result = buildMessage(projects, sha)
     expect(result).toEqual(expected2Projects)
   })
+
+  it("returns correct message when projects don't have coverage before", () => {
+    const projects: CoveredProject[] = [
+      { ...projectA, coverageBefore: undefined },
+      { ...projectB, coverageBefore: undefined }
+    ]
+    const sha = 'abcdef1234567890'
+    const result = buildMessage(projects, sha)
+    expect(result).toEqual(expected2ProjectsNoBefore)
+  })
 })
 
 const expected1Project = `# Coverage Report
@@ -89,6 +99,44 @@ Description B
 ![0% - fail](http://img.shields.io/badge/project__b-0.00%25-critical)    ➡️ 0.00%
 
 
+<details>
+<summary>Coverage Details for <strong>project_b</strong></summary>
+
+| File | Line Percentage | Line Count |
+| --- | --- | --- |
+
+</details>
+
+`
+
+const expected2ProjectsNoBefore = `# Coverage Report
+This is an automatic coverage report for abcdef12, proudly generated by [Dart Coverage Assistant](https://github.com/whynotmake-it/dart-coverage-assistant) 🎯🧪.
+
+## Monorepo coverage
+This repository contains 2 Dart projects. This is is the total coverage across all of them:
+
+![0% - fail](http://img.shields.io/badge/0.00%25-critical)    
+
+## \`project_a\`
+Description A
+
+![0% - fail](http://img.shields.io/badge/project__a-0.00%25-critical)    
+
+
+<details>
+<summary>Coverage Details for <strong>project_a</strong></summary>
+
+| File | Line Percentage | Line Count |
+| --- | --- | --- |
+
+</details>
+
+## \`project_b\`
+Description B
+
+![0% - fail](http://img.shields.io/badge/project__b-0.00%25-critical)    
+
+
 <details>
 <summary>Coverage Details for <strong>project_b</strong></summary>
 

src/lcov.ts

@@ -119,8 +119,11 @@ export function getTotalPercentage(
 
 export function getTotalPercentageBefore(
   projects: CoveredProject[]
-): LineCoverage {
-  return getLineCoverage(getSectionSummaries(projects, 'coverageBefore'))
+): LineCoverage | undefined {
+  if (projects.some(p => p.coverageBefore !== undefined)) {
+    return getLineCoverage(getSectionSummaries(projects, 'coverageBefore'))
+  }
+  return undefined
 }
 
 function getSectionSummaries(