Enable asserts when testing pub (#2754)

diff --git a/lib/src/entrypoint.dart b/lib/src/entrypoint.dart
index 127bc0a..3c949c3 100644
--- a/lib/src/entrypoint.dart
+++ b/lib/src/entrypoint.dart
@@ -740,6 +740,7 @@
     // Check if language version specified in the `package_config.json` is
     // correct. This is important for path dependencies as these can mutate.
     for (final pkg in cfg.packages) {
+      if (pkg.name == root.name || pkg.name == 'flutter_gen') continue;
       final id = lockFile.packages[pkg.name];
       if (id == null) {
         assert(
diff --git a/lib/src/null_safety_analysis.dart b/lib/src/null_safety_analysis.dart
index ab9777e..746999c 100644
--- a/lib/src/null_safety_analysis.dart
+++ b/lib/src/null_safety_analysis.dart
@@ -174,7 +174,7 @@
               .createContext(
                 sdkPath: getSdkPath(),
                 contextRoot: ContextLocator().locateRoots(
-                  includedPaths: [packageDir],
+                  includedPaths: [path.normalize(packageDir)],
                 ).first,
               )
               .currentSession;
diff --git a/lib/src/solver/failure.dart b/lib/src/solver/failure.dart
index 3bdc645..a23b1fa 100644
--- a/lib/src/solver/failure.dart
+++ b/lib/src/solver/failure.dart
@@ -37,7 +37,8 @@
   }
 
   SolveFailure(this.incompatibility)
-      : assert(incompatibility.terms.single.package.isRoot);
+      : assert(incompatibility.terms.isEmpty ||
+            incompatibility.terms.single.package.isRoot);
 
   /// Describes how [incompatibility] was derived, and thus why version solving
   /// failed.
diff --git a/test/test_pub.dart b/test/test_pub.dart
index f780f3b..d757cb6 100644
--- a/test/test_pub.dart
+++ b/test/test_pub.dart
@@ -450,7 +450,7 @@
 
   final dotPackagesPath = (await Isolate.packageConfig).toString();
 
-  var dartArgs = ['--packages=$dotPackagesPath'];
+  var dartArgs = ['--packages=$dotPackagesPath', '--enable-asserts'];
   dartArgs..addAll([pubPath, if (verbose) '--verbose'])..addAll(args);
 
   return await PubProcess.start(dartBin, dartArgs,