Add support for single-writer databases to unit test.

permazen-kv-test/src/main/java/io/permazen/kv/test/KVDatabaseTest.java

@@ -84,26 +84,56 @@ protected KVDatabase[][] getDBs() {
 
     protected abstract KVDatabase getKVDatabase();
 
+    // How many transactions in testNonconflictingTransactions()?
     protected int getNonconflictingTransactionCount() {
         return 10;
     }
 
+    // How many loops in testParallelTransactions()?
     protected int getParallelTransactionLoopCount() {
         return 25;
     }
 
+    // How many transactions in testParallelTransactions()?
     protected int getParallelTransactionTaskCount() {
         return 25;
     }
 
+    // How many transactions in testSequentialTransactions()?
     protected int getSequentialTransactionLoopCount() {
         return 50;
     }
 
+    // How many iterations in RandomTask?
     protected int getRandomTaskMaxIterations() {
         return 1000;
     }
 
+    // Does this database permit write skew anomalies?
+    protected boolean allowsWriteSkewAnomaly() {
+        return false;
+    }
+
+    // Does this database allow tx.setReadOnly() after data has been accessed?
+    protected boolean supportsReadOnlyAfterDataAccess() {
+        return true;
+    }
+
+    // When there's a conflict, is it OK if BOTH transactions fail?
+    protected boolean allowBothTransactionsToFail() {
+        return false;
+    }
+
+    // Does this database tolerate multiple threads accessing a single transaction?
+    protected boolean transactionsAreThreadSafe() {
+        return true;
+    }
+
+    // Does this database support multiple simulatenous write transactions?
+    protected boolean supportsMultipleWriteTransactions() {
+        return true;
+    }
+
     @Test(dataProvider = "kvdbs")
     public void testSimpleStuff(KVDatabase store) throws Exception {
 
@@ -241,10 +271,6 @@ public void testReadOnly(KVDatabase store) throws Exception {
         }
     }
 
-    protected boolean supportsReadOnlyAfterDataAccess() {
-        return true;
-    }
-
     private byte[] randomBytes(int index) {
         final byte[] array = new byte[this.random.nextInt(10) + 1];
         this.random.nextBytes(array);
@@ -405,13 +431,15 @@ public void testWriteSkewAnomaly(KVDatabase store) throws Exception {
         }, kv("10", "01"), kv("20", "02"));
     }
 
-    protected boolean allowsWriteSkewAnomaly() {
-        return false;
-    }
-
     protected void testConflictingTransactions(KVDatabase store, String name,
       Conflictor conflictor, KVPair expected1, KVPair expected2) throws Exception {
 
+        // Conflicts handled?
+        if (!this.supportsMultipleWriteTransactions()) {
+            this.log.info("skipping " + name + "() on " + store + ": database doesn't support simultaneous writers");
+            return;
+        }
+
         // Clear database
         this.log.info("starting {}() on {}", name, store);
         this.tryNtimes(store, tx -> tx.removeRange(null, null));
@@ -520,12 +548,12 @@ private interface Conflictor {
         Future<?>[] conflict(KVTransaction tx1, KVTransaction tx2) throws Exception;
     }
 
-    protected boolean allowBothTransactionsToFail() {
-        return false;
-    }
-
     @Test(dataProvider = "kvdbs")
     public void testNonconflictingTransactions(KVDatabase store) throws Exception {
+        if (!this.supportsMultipleWriteTransactions()) {
+            this.log.info("skipping testNonconflictingTransactions() on " + store + ": database doesn't support simultaneous writers");
+            return;
+        }
 
         // Clear database
         this.log.info("starting testNonconflictingTransactions() on " + store);
@@ -593,6 +621,10 @@ public void testNonconflictingTransactions(KVDatabase store) throws Exception {
      */
     @Test(dataProvider = "kvdbs")
     public void testParallelTransactions(KVDatabase store) throws Exception {
+        if (!this.supportsMultipleWriteTransactions()) {
+            this.log.info("skipping testParallelTransactions() on " + store + ": database doesn't support simultaneous writers");
+            return;
+        }
         this.testParallelTransactions(new KVDatabase[] { store });
     }
 
@@ -714,10 +746,6 @@ public void testMultipleThreadsTransaction(KVDatabase store) throws Exception {
         this.log.info("finished testMultipleThreadsTransaction() on " + store);
     }
 
-    protected boolean transactionsAreThreadSafe() {
-        return true;
-    }
-
     /**
      * Test KVStore.apply().
      *