Improve diagnostic for PrepareDepsOfTargetsUnderDirectoryFunctionTest

We've been hitting a (flaky?) bug in CI that we haven't been able to reproduce locally yet. The failure is here, so this assertion change should help us see what the actual error message is.

PiperOrigin-RevId: 355062974
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/PrepareDepsOfTargetsUnderDirectoryFunctionTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/PrepareDepsOfTargetsUnderDirectoryFunctionTest.java
index 1cf347f..d83878e 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/PrepareDepsOfTargetsUnderDirectoryFunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/PrepareDepsOfTargetsUnderDirectoryFunctionTest.java
@@ -15,6 +15,7 @@
 package com.google.devtools.build.lib.skyframe;
 
 import static com.google.common.truth.Truth.assertThat;
+import static com.google.devtools.build.skyframe.EvaluationResultSubjectFactory.assertThatEvaluationResult;
 import static com.google.devtools.build.skyframe.WalkableGraphUtils.exists;
 
 import com.google.common.base.Preconditions;
@@ -82,7 +83,7 @@
             .build();
     EvaluationResult<PrepareDepsOfTargetsUnderDirectoryValue> evaluationResult =
         skyframeExecutor.getDriver().evaluate(ImmutableList.copyOf(keys), evaluationContext);
-    Preconditions.checkState(!evaluationResult.hasError());
+    assertThatEvaluationResult(evaluationResult).hasNoError();
     return evaluationResult;
   }