File paths in TestContext are relative, not absolute (#1843)

Author: elliette

dwds/test/dart_uri_file_uri_test.dart

@@ -23,7 +23,10 @@ final context = TestContext(
 final dwdsDir = Directory.current.absolute.path;
 
 /// The directory for the general _test package.
-final testDir = p.join(p.dirname(dwdsDir), 'fixtures', '_test');
+final testDir = p.normalize(p.absolute(p.relative(
+  p.join('..', 'fixtures', '_test'),
+  from: p.current,
+)));
 
 /// The directory for the _testPackage package (contained within dwds), which
 /// imports _test.

dwds/test/fixtures/context.dart

@@ -121,14 +121,14 @@ class TestContext {
     this.path = 'hello_world/index.html',
     this.pathToServe = 'example',
   }) {
-    final packageName = nullSafety == NullSafety.sound ? '_testSound' : '_test';
-    final relativeDirectory = p.join('..', 'fixtures', packageName);
+    final defaultPackage =
+        nullSafety == NullSafety.sound ? '_testSound' : '_test';
+    final defaultDirectory = p.join('..', 'fixtures', defaultPackage);
+    final defaultEntry = p.join('..', 'fixtures', defaultPackage, 'example',
+        'append_body', 'main.dart');
 
-    final relativeEntry = p.join(
-        '..', 'fixtures', packageName, 'example', 'append_body', 'main.dart');
-
-    workingDirectory = p.normalize(p
-        .absolute(directory ?? p.relative(relativeDirectory, from: p.current)));
+    workingDirectory = p.normalize(
+        p.absolute(p.relative(directory ?? defaultDirectory, from: p.current)));
 
     DartUri.currentDirectory = workingDirectory;
 
@@ -138,7 +138,7 @@ class TestContext {
         p.toUri(p.join(workingDirectory, '.dart_tool/package_config.json'));
 
     final entryFilePath = p.normalize(
-        p.absolute(entry ?? p.relative(relativeEntry, from: p.current)));
+        p.absolute(p.relative(entry ?? defaultEntry, from: p.current)));
 
     _logger.info('Serving: $pathToServe/$path');
     _logger.info('Project: $_projectDirectory');