Apply hard-coded contract to TestVerb.that

… to support TestVerb-returning methods like TruthJUnit4.assume,
Truth.assert_, and Truth.assertWithMessage, in statements like
assume().that(…).isNotNull().

Change-Id: Idbb1e9cfe6e58b067577fffc4ed301807ebbab9d

java/java-tests/testData/inspection/dataFlow/fixture/GoogleTruth.java

@@ -1,6 +1,7 @@
 import org.jetbrains.annotations.Nullable;
 
 import static com.google.common.truth.Truth.assertThat;
+import static com.google.common.truth.TruthJUnit.assume;
 
 class Contracts {
 
@@ -9,4 +10,8 @@ class Contracts {
     System.out.println(o.hashCode());
   }
 
+  private void assumeNotNullValue(@Nullable Object o) {
+    assume().that(o).isNotNull();
+    System.out.println(o.hashCode());
+  }
 }