Add tests for the ConflictDetection utility class

error-prone-contrib/src/main/java/tech/picnic/errorprone/bugpatterns/util/MoreJUnitMatchers.java

@@ -23,7 +23,7 @@
 import com.sun.tools.javac.code.Type;
 import java.util.Optional;
 import javax.lang.model.type.TypeKind;
-import org.jspecify.nullness.Nullable;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A collection of JUnit-specific helper methods and {@link Matcher}s.

error-prone-contrib/src/test/java/tech/picnic/errorprone/bugpatterns/util/ConflictDetectionTest.java

@@ -0,0 +1,56 @@
+package tech.picnic.errorprone.bugpatterns.util;
+
+import static com.google.errorprone.BugPattern.SeverityLevel.ERROR;
+
+import com.google.errorprone.BugPattern;
+import com.google.errorprone.CompilationTestHelper;
+import com.google.errorprone.VisitorState;
+import com.google.errorprone.bugpatterns.BugChecker;
+import com.google.errorprone.matchers.Description;
+import com.sun.source.tree.MethodTree;
+import org.junit.jupiter.api.Test;
+
+final class ConflictDetectionTest {
+  @Test
+  void matcher() {
+    CompilationTestHelper.newInstance(RenameBlockerFlagger.class, getClass())
+        .addSourceLines(
+            "/A.java",
+            "class A {",
+            "  private void foo1() {}",
+            "",
+            "  // BUG: Diagnostic contains: [RenameBlockerFlagger] a method named `foo2t` already exists in this",
+            "  // class",
+            "  private void foo2() {}",
+            "",
+            "  private void foo2t() {}",
+            "",
+            "  // BUG: Diagnostic contains: [RenameBlockerFlagger] `foo3t` is already statically imported",
+            "  private void foo3() {}",
+            "",
+            "  // BUG: Diagnostic contains: [RenameBlockerFlagger] `int` is a reserved keyword",
+            "  private void in() {}",
+            "}")
+        .addSourceLines(
+            "/staticimport/B.java",
+            "package staticimport;",
+            "",
+            "public class B {",
+            "  public static void foo3t() {}",
+            "}")
+        .doTest();
+  }
+
+  @BugPattern(summary = "Flags blockers for renaming methods", severity = ERROR)
+  public static final class RenameBlockerFlagger extends BugChecker
+      implements BugChecker.MethodTreeMatcher {
+    private static final long serialVersionUID = 1L;
+
+    @Override
+    public Description matchMethod(MethodTree tree, VisitorState state) {
+      return ConflictDetection.findMethodRenameBlocker(tree.getName() + "t", state)
+          .map(blocker -> buildDescription(tree).setMessage(blocker).build())
+          .orElse(Description.NO_MATCH);
+    }
+  }
+}