Add marginal price capability and update integration tests

Balancer now passes the test
Some misc aesthetics

evm/src/balancer-v2/BalancerV2SwapAdapter.sol

@@ -188,11 +188,10 @@ contract BalancerV2SwapAdapter is ISwapAdapter {
         override
         returns (Capability[] memory capabilities)
     {
-        capabilities = new Capability[](4);
+        capabilities = new Capability[](3);
         capabilities[0] = Capability.SellOrder;
         capabilities[1] = Capability.BuyOrder;
         capabilities[2] = Capability.PriceFunction;
-        capabilities[3] = Capability.HardLimits;
     }
 
     function getTokens(bytes32 poolId)

evm/src/interfaces/ISwapAdapterTypes.sol

@@ -33,7 +33,11 @@ interface ISwapAdapterTypes {
         ScaledPrices,
         // Indicates that if we try to go over the sell limits, the pool will
         // revert (optional)
-        HardLimits
+        HardLimits,
+        // Indicates whether the pool's price function can be called with
+        // amountIn=0 to return the
+        // current price (optional)
+        MarginalPrice
     }
 
     /// @dev Representation used for rational numbers such as prices.

evm/test/AdapterTest.sol

@@ -11,7 +11,7 @@ contract AdapterTest is Test, ISwapAdapterTypes {
     using FractionMath for Fraction;
 
     uint256 constant pricePrecision = 10e24;
-    string[] public stringPctgs = ["0%", "0.01%", "50%", "100%"];
+    string[] public stringPctgs = ["0%", "0.1%", "50%", "100%"];
 
     // @notice Test the behavior of a swap adapter for a list of pools
     // @dev Computes limits, prices, and swaps on the pools on both directions
@@ -29,6 +29,7 @@ contract AdapterTest is Test, ISwapAdapterTypes {
         for (uint256 i = 0; i < poolIds.length; i++) {
             address[] memory tokens = adapter.getTokens(poolIds[i]);
             IERC20(tokens[0]).approve(address(adapter), type(uint256).max);
+            IERC20(tokens[1]).approve(address(adapter), type(uint256).max);
 
             testPricesForPair(
                 adapter, poolIds[i], tokens[0], tokens[1], hasPriceImpact
@@ -59,7 +60,13 @@ contract AdapterTest is Test, ISwapAdapterTypes {
             tokenOut,
             sellLimit
         );
-        uint256[] memory amounts = calculateTestAmounts(sellLimit);
+
+        bool hasMarginalPrices = hasCapability(
+            adapter.getCapabilities(poolId, tokenIn, tokenOut),
+            Capability.MarginalPrice
+        );
+        uint256[] memory amounts =
+            calculateTestAmounts(sellLimit, hasMarginalPrices);
         Fraction[] memory prices =
             adapter.price(poolId, tokenIn, tokenOut, amounts);
         assertGt(
@@ -78,17 +85,15 @@ contract AdapterTest is Test, ISwapAdapterTypes {
         assertGt(prices[0].denominator, 0, "Denominator shouldn't be 0");
 
         Trade memory trade;
-        deal(tokenIn, address(this), 2 * amounts[amounts.length - 1]);
+        deal(tokenIn, address(this), 5 * amounts[amounts.length - 1]);
 
         for (uint256 j = 1; j < amounts.length; j++) {
             console2.log(
-                "TEST: Testing behavior for price at %s of limit: %d",
+                "TEST: Testing behavior for price at %s of limit.",
                 stringPctgs[j],
                 amounts[j]
             );
             uint256 priceAtAmount = fractionToInt(prices[j]);
-            assertGt(prices[j].numerator, 0, "Nominator shouldn't be 0");
-            assertGt(prices[j].denominator, 0, "Denominator shouldn't be 0");
 
             console2.log("TEST: Swapping %d of %s", amounts[j], tokenIn);
             trade = adapter.swap(
@@ -97,12 +102,12 @@ contract AdapterTest is Test, ISwapAdapterTypes {
             uint256 executedPrice =
                 trade.calculatedAmount * pricePrecision / amounts[j];
             uint256 priceAfterSwap = fractionToInt(trade.price);
-            console2.log("TEST: Pool price:       %d", priceAtAmount);
+            console2.log("TEST:  - Pool price:       %d", priceAtAmount);
-            console2.log("TEST: Executed price:   %d", executedPrice);
+            console2.log("TEST:  - Executed price:   %d", executedPrice);
-            console2.log("TEST: Price after swap: %d", priceAfterSwap);
+            console2.log("TEST:  - Price after swap: %d", priceAfterSwap);
 
             if (hasPriceImpact) {
-                assertGt(
+                assertGe(
                     priceAtAmount,
                     executedPrice,
                     "Price should be greated than executed price."
@@ -121,17 +126,17 @@ contract AdapterTest is Test, ISwapAdapterTypes {
                 assertGe(
                     priceAtAmount,
                     executedPrice,
-                    "Price should be greated than executed price."
+                    "Price should be greater or equal to executed price."
                 );
                 assertGe(
                     executedPrice,
                     priceAfterSwap,
-                    "Executed price should be greater than price after swap."
+                    "Executed price should be or equal to price after swap."
                 );
                 assertGe(
                     priceAtAmount,
                     priceAfterSwap,
-                    "Price should be greated than price after swap."
+                    "Price should be or equal to price after swap."
                 );
             }
         }
@@ -151,6 +156,8 @@ contract AdapterTest is Test, ISwapAdapterTypes {
                 adapter, poolId, tokenIn, tokenOut, amountAboveLimit
             );
         }
+
+        console2.log("TEST: All tests passed.");
     }
 
     function testRevertAboveLimit(
@@ -165,7 +172,9 @@ contract AdapterTest is Test, ISwapAdapterTypes {
         aboveLimitArray[0] = amountAboveLimit;
 
         try adapter.price(poolId, tokenIn, tokenOut, aboveLimitArray) {
-            revert("Pool shouldn't be fetch prices above the sell limit");
+            revert(
+                "Pool shouldn't be able to fetch prices above the sell limit"
+            );
         } catch Error(string memory s) {
             console2.log(
                 "TEST: Expected error when fetching price above limit: %s", s
@@ -199,14 +208,14 @@ contract AdapterTest is Test, ISwapAdapterTypes {
         );
     }
 
-    function calculateTestAmounts(uint256 limit)
+    function calculateTestAmounts(uint256 limit, bool hasMarginalPrices)
         internal
         pure
         returns (uint256[] memory)
     {
         uint256[] memory amounts = new uint256[](4);
-        amounts[0] = 0;
+        amounts[0] = hasMarginalPrices ? 0 : limit / 10000;
-        amounts[1] = limit / 10000;
+        amounts[1] = limit / 1000;
         amounts[2] = limit / 2;
         amounts[3] = limit;
         return amounts;