Make --test_sharding_strategy=forced=k have a deterministic options…

… checksum.

`TestShardingStrategyForced` didn't implement `toString`, so an incremental build with `--test_sharding_strategy=forced=k` with no change to `k` was invalidating all test targets (or all configured targets if `--notrim_test_configuration`).

PiperOrigin-RevId: 718512597
Change-Id: I2dc174e02f5a072ea0378d87c30d26e55173b651

src/main/java/com/google/devtools/build/lib/analysis/test/TestShardingStrategyForced.java

@@ -25,4 +25,9 @@ final class TestShardingStrategyForced implements TestShardingStrategy {
   public int getNumberOfShards(int shardCountFromAttr) {
     return forcedShardsCount;
   }
+
+  @Override
+  public String toString() {
+    return "forced=" + forcedShardsCount;
+  }
 }

src/test/java/com/google/devtools/build/lib/analysis/test/TestActionBuilderTest.java

@@ -248,6 +248,32 @@ public void testShardingForced() throws Exception {
     assertSharded(getConfiguredTarget("//javatests/jt:RGT_many"), 5);
   }
 
+  @Test
+  public void testShardingForced_equalValue_equalChecksum() throws Exception {
+    useConfiguration("--test_sharding_strategy=forced=5");
+    var config1 = getTargetConfiguration();
+
+    initializeSkyframeExecutor();
+
+    useConfiguration("--test_sharding_strategy=forced=5");
+    var config2 = getTargetConfiguration();
+
+    assertThat(config2).isEqualTo(config1);
+  }
+
+  @Test
+  public void testShardingForced_differentValue_differentChecksum() throws Exception {
+    useConfiguration("--test_sharding_strategy=forced=5");
+    var config1 = getTargetConfiguration();
+
+    initializeSkyframeExecutor();
+
+    useConfiguration("--test_sharding_strategy=forced=6");
+    var config2 = getTargetConfiguration();
+
+    assertThat(config2).isNotEqualTo(config1);
+  }
+
   @Test
   public void testFlakyAttributeValidation() throws Exception {
     scratch.file(