Fix isInf() overload method and add tests

src/main/java/build/buf/protovalidate/internal/celext/CustomOverload.java

@@ -329,7 +329,12 @@ private static Overload isInf() {
         value -> value.convertToNative(Double.TYPE).isInfinite() ? BoolT.True : BoolT.False,
         (lhs, rhs) -> {
           Double value = lhs.convertToNative(Double.TYPE);
-          return value.isInfinite(rhs.intValue()) ? BoolT.True : BoolT.False;
+          long sign = rhs.intValue();
+          if (sign == 0) {
+            return value.isInfinite() ? BoolT.True : BoolT.False;
+          }
+          double expectedValue = (sign > 0) ? Double.POSITIVE_INFINITY : Double.NEGATIVE_INFINITY;
+          return value == expectedValue ? BoolT.True : BoolT.False;
         },
         null);
   }

src/test/java/build/buf/protovalidate/internal/celext/CustomOverloadTest.java

@@ -0,0 +1,62 @@
+package build.buf.protovalidate.internal.celext;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.google.common.collect.ImmutableMap;
+import java.util.Map;
+import org.junit.Test;
+import org.projectnessie.cel.Ast;
+import org.projectnessie.cel.Env;
+import org.projectnessie.cel.Library;
+import org.projectnessie.cel.Program;
+import org.projectnessie.cel.interpreter.Activation;
+
+public class CustomOverloadTest {
+
+  private final Env env = Env.newEnv(Library.Lib(new ValidateLibrary()));
+
+  @Test
+  public void testIsInf() {
+    Map<String, Boolean> testCases =
+        ImmutableMap.<String, Boolean>builder()
+            .put("0.0.isInf()", false)
+            .put("(1.0/0.0).isInf()", true)
+            .put("(1.0/0.0).isInf(0)", true)
+            .put("(1.0/0.0).isInf(1)", true)
+            .put("(1.0/0.0).isInf(-1)", false)
+            .put("(-1.0/0.0).isInf()", true)
+            .put("(-1.0/0.0).isInf(0)", true)
+            .put("(-1.0/0.0).isInf(1)", false)
+            .put("(-1.0/0.0).isInf(-1)", true)
+            .build();
+    for (Map.Entry<String, Boolean> testCase : testCases.entrySet()) {
+      Program.EvalResult result = eval(testCase.getKey());
+      assertThat(result.getVal().booleanValue()).isEqualTo(testCase.getValue());
+    }
+  }
+
+  @Test
+  public void testIsNan() {
+    Map<String, Boolean> testCases =
+        ImmutableMap.<String, Boolean>builder()
+            .put("0.0.isNan()", false)
+            .put("(0.0/0.0).isNan()", true)
+            .put("(1.0/0.0).isNan()", false)
+            .build();
+    for (Map.Entry<String, Boolean> testCase : testCases.entrySet()) {
+      Program.EvalResult result = eval(testCase.getKey());
+      assertThat(result.getVal().booleanValue()).isEqualTo(testCase.getValue());
+    }
+  }
+
+  private Program.EvalResult eval(String source) {
+    return eval(source, Activation.emptyActivation());
+  }
+
+  private Program.EvalResult eval(String source, Object vars) {
+    Env.AstIssuesTuple parsed = env.parse(source);
+    assertThat(parsed.hasIssues()).isFalse();
+    Ast ast = parsed.getAst();
+    return env.program(ast).eval(vars);
+  }
+}