Gracefully handle empty failure tags

This commit fixes #137. Some JUnit generators emit an empty failure tag,
with only a message property set. In those cases, the parser crashes
when trying to match the failure with a source file. Since this feature
is optional, the simplest fix is to skip the processing when the failure
tag is empty.

Also added a test, and the corresponding input file is generated from a
reporter within our codebase.

__tests__/fixtures/external/java/empty_failures.xml

@@ -0,0 +1,2 @@
+<?xml version='1.0' encoding='utf-8'?>
+<testsuites name="my_package.test_foo" tests="3" failures="1" errors="0" time="6.79"><testsuite name="my_package.test_foo.launch_tests" tests="3" failures="1" errors="0" skipped="0" time="6.79"><testcase classname="my_package.TestFoo" name="test_normal_case" time="2.172" /><testcase classname="my_package.TestFoo" name="test_other_case" time="4.558"><failure message="Traceback (most recent call last):&#10;  File &quot;/home/redacted/test_foo.py&quot;, line 183, in test_other_case&#10;    self.assertFalse(True)&#10;AssertionError: True is not false&#10;" /></testcase><testcase classname="my_package.TestFoo" name="test_yet_another_case" time="0.06" /></testsuite></testsuites>

__tests__/java-junit.test.ts

@@ -72,4 +72,22 @@ describe('java-junit tests', () => {
     fs.mkdirSync(path.dirname(outputPath), {recursive: true})
     fs.writeFileSync(outputPath, report)
   })
+
+  it('parses empty failures in test results', async () => {
+    const fixturePath = path.join(__dirname, 'fixtures', 'external', 'java', 'empty_failures.xml')
+    const filePath = normalizeFilePath(path.relative(__dirname, fixturePath))
+    const fileContent = fs.readFileSync(fixturePath, {encoding: 'utf8'})
+
+    const trackedFiles: string[] = []
+    const opts: ParseOptions = {
+      parseErrors: true,
+      trackedFiles
+    }
+
+    const parser = new JavaJunitParser(opts)
+    const result = await parser.parse(filePath, fileContent)
+
+    expect(result.result === 'failed')
+    expect(result.failed === 1)
+  })
 })

src/parsers/java-junit/java-junit-parser.ts

@@ -128,10 +128,13 @@ export class JavaJunitParser implements TestParser {
     let filePath
     let line
 
-    const src = this.exceptionThrowSource(details)
-    if (src) {
-      filePath = src.filePath
-      line = src.line
+    if(details != null)
+    {
+      const src = this.exceptionThrowSource(details)
+      if (src) {
+        filePath = src.filePath
+        line = src.line
+      }
     }
 
     return {