test(spanner): replace fixed hashCode value assertions with contract-compliance tests in OptionsTest

`OptionsTest` contained four assertions that verified `Options#hashCode()` returns specific fixed integer values (31, 108027089, -2118248262). The Java `hashCode()` contract does not guarantee cross-JVM or cross-version stability of hash values, so testing against hardcoded numbers is brittle and misleads readers into thinking fixed values are part of the API contract.

Signed-off-by: anish k <ak8686@princeton.edu>

Author: anishesg

java-spanner/google-cloud-spanner/src/test/java/com/google/cloud/spanner/OptionsTest.java

@@ -152,7 +152,11 @@ public void allOptionsAbsent() {
     assertThat(options.equals(null)).isFalse();
     assertThat(options.equals(this)).isFalse();
     assertNull(options.isolationLevel());
-    assertThat(options.hashCode()).isEqualTo(31);
+    // Verify hashCode contract: equal objects must have equal hashCodes, and hashCode is stable.
+    Options options2 = Options.fromReadOptions();
+    assertThat(options.equals(options2)).isTrue();
+    assertThat(options.hashCode()).isEqualTo(options2.hashCode());
+    assertThat(options.hashCode()).isEqualTo(options.hashCode());
   }
 
   @Test
@@ -175,7 +179,13 @@ public void listOptionsTest() {
     assertThat(options.pageSize()).isEqualTo(pageSize);
     assertThat(options.pageToken()).isEqualTo(pageToken);
     assertThat(options.filter()).isEqualTo(filter);
-    assertThat(options.hashCode()).isEqualTo(108027089);
+    // Verify hashCode contract: equal objects must have equal hashCodes, and hashCode is stable.
+    Options options2 =
+        Options.fromListOptions(
+            Options.pageSize(pageSize), Options.pageToken(pageToken), Options.filter(filter));
+    assertThat(options.equals(options2)).isTrue();
+    assertThat(options.hashCode()).isEqualTo(options2.hashCode());
+    assertThat(options.hashCode()).isEqualTo(options.hashCode());
   }
 
   @Test
@@ -696,7 +706,11 @@ public void updateOptionsTest() {
     assertEquals("tag: " + tag + " ", options.toString());
     assertTrue(options.hasTag());
     assertThat(options.tag()).isEqualTo(tag);
-    assertThat(options.hashCode()).isEqualTo(-2118248262);
+    // Verify hashCode contract: equal objects must have equal hashCodes, and hashCode is stable.
+    Options options2 = Options.fromUpdateOptions(Options.tag(tag));
+    assertThat(options.equals(options2)).isTrue();
+    assertThat(options.hashCode()).isEqualTo(options2.hashCode());
+    assertThat(options.hashCode()).isEqualTo(options.hashCode());
   }
 
   @Test
@@ -728,7 +742,11 @@ public void transactionOptionsTest() {
     assertEquals("tag: " + tag + " ", options.toString());
     assertTrue(options.hasTag());
     assertThat(options.tag()).isEqualTo(tag);
-    assertThat(options.hashCode()).isEqualTo(-2118248262);
+    // Verify hashCode contract: equal objects must have equal hashCodes, and hashCode is stable.
+    Options options2 = Options.fromTransactionOptions(Options.tag(tag));
+    assertThat(options.equals(options2)).isTrue();
+    assertThat(options.hashCode()).isEqualTo(options2.hashCode());
+    assertThat(options.hashCode()).isEqualTo(options.hashCode());
   }
 
   @Test