refactor: reorganize tests

src/DSPC.t.sol

@@ -3,7 +3,7 @@ pragma solidity ^0.8.24;
 
 import {Test} from "forge-std/Test.sol";
 import {DSPC} from "./DSPC.sol";
-import {Rates} from "./test/Rates.sol";
+import {RatesMock} from "./mocks/RatesMock.sol";
 
 contract MockJug {
     mapping(bytes32 => uint256) public duty;
@@ -38,10 +38,10 @@ contract MockSUSDS {
 
 contract MockConv {
     uint256 constant RAY = 1e27;
-    Rates public rates;
+    RatesMock public rates;
 
     constructor() {
-        rates = new Rates();
+        rates = new RatesMock();
     }
 
     function turn(uint256 bps) external view returns (uint256) {
@@ -50,7 +50,15 @@ contract MockConv {
     }
 }
 
-contract DSPCTest is Test {
+contract DSPCHarness is DSPC {
+    constructor(address _jug, address _pot, address _susds, address _conv) DSPC(_jug, _pot, _susds, _conv) {}
+
+    function exposed_back(uint256 ray) public pure returns (uint256) {
+        return _back(ray);
+    }
+}
+
+contract DSPCTest is Test, RatesMock {
     // --- Events ---
     event Rely(address indexed usr);
     event Deny(address indexed usr);
@@ -62,7 +70,7 @@ contract DSPCTest is Test {
     event Zap();
     event Halt();
 
-    DSPC dspc;
+    DSPCHarness dspc;
     MockJug jug;
     MockPot pot;
     MockSUSDS susds;
@@ -81,7 +89,7 @@ contract DSPCTest is Test {
         pot = new MockPot();
         susds = new MockSUSDS();
         conv = new MockConv();
-        dspc = new DSPC(address(jug), address(pot), address(susds), address(conv));
+        dspc = new DSPCHarness(address(jug), address(pot), address(susds), address(conv));
 
         // Initialize mock rates
         jug.file(ILK, "duty", conv.turn(100)); // 1%
@@ -272,4 +280,116 @@ contract DSPCTest is Test {
         assertEq(storedUpdates.length, 1);
         assertEq(eta, block.timestamp + 1 days);
     }
+
+    function test_back() public {
+        uint256[] memory validKeys = new uint256[](450);
+        uint256 idx;
+
+        // Add all keys that exist in the mapping
+        validKeys[idx++] = 0;
+        validKeys[idx++] = 1;
+        validKeys[idx++] = 2;
+        validKeys[idx++] = 5;
+        validKeys[idx++] = 6;
+        validKeys[idx++] = 10;
+        validKeys[idx++] = 25;
+        validKeys[idx++] = 50;
+        validKeys[idx++] = 75;
+        validKeys[idx++] = 100;
+        validKeys[idx++] = 125;
+        validKeys[idx++] = 133;
+        validKeys[idx++] = 150;
+        validKeys[idx++] = 175;
+        validKeys[idx++] = 200;
+        validKeys[idx++] = 225;
+        validKeys[idx++] = 250;
+        validKeys[idx++] = 275;
+        validKeys[idx++] = 300;
+        validKeys[idx++] = 319;
+        validKeys[idx++] = 325;
+        validKeys[idx++] = 333;
+        validKeys[idx++] = 344;
+        validKeys[idx++] = 345;
+        validKeys[idx++] = 349;
+        validKeys[idx++] = 350;
+        validKeys[idx++] = 358;
+        validKeys[idx++] = 370;
+        validKeys[idx++] = 374;
+        validKeys[idx++] = 375;
+        validKeys[idx++] = 394;
+        validKeys[idx++] = 400;
+        validKeys[idx++] = 408;
+        validKeys[idx++] = 420;
+        validKeys[idx++] = 424;
+        validKeys[idx++] = 425;
+        validKeys[idx++] = 450;
+        validKeys[idx++] = 475;
+        validKeys[idx++] = 490;
+        validKeys[idx++] = 500;
+        validKeys[idx++] = 520;
+        validKeys[idx++] = 525;
+        validKeys[idx++] = 537;
+        validKeys[idx++] = 544;
+        validKeys[idx++] = 550;
+        validKeys[idx++] = 554;
+        validKeys[idx++] = 555;
+        validKeys[idx++] = 561;
+        validKeys[idx++] = 569;
+        validKeys[idx++] = 575;
+        validKeys[idx++] = 579;
+        validKeys[idx++] = 580;
+        validKeys[idx++] = 586;
+        validKeys[idx++] = 600;
+        validKeys[idx++] = 616;
+        validKeys[idx++] = 619;
+        validKeys[idx++] = 625;
+        validKeys[idx++] = 629;
+        validKeys[idx++] = 630;
+        validKeys[idx++] = 636;
+        validKeys[idx++] = 640;
+        validKeys[idx++] = 641;
+        validKeys[idx++] = 643;
+        validKeys[idx++] = 645;
+        validKeys[idx++] = 649;
+        validKeys[idx++] = 650;
+        validKeys[idx++] = 665;
+        validKeys[idx++] = 668;
+        validKeys[idx++] = 670;
+        validKeys[idx++] = 674;
+        validKeys[idx++] = 675;
+        validKeys[idx++] = 691;
+        validKeys[idx++] = 700;
+        validKeys[idx++] = 716;
+        validKeys[idx++] = 718;
+        validKeys[idx++] = 720;
+        validKeys[idx++] = 724;
+        validKeys[idx++] = 725;
+        validKeys[idx++] = 750;
+        validKeys[idx++] = 775;
+        validKeys[idx++] = 800;
+        validKeys[idx++] = 825;
+        validKeys[idx++] = 850;
+        validKeys[idx++] = 875;
+        validKeys[idx++] = 900;
+        validKeys[idx++] = 925;
+        validKeys[idx++] = 931;
+        validKeys[idx++] = 950;
+        validKeys[idx++] = 975;
+        validKeys[idx++] = 1000;
+
+        // Add all remaining multiples of 25 from 1025 to 10000
+        for (uint256 i = 1025; i <= 10000; i += 25) {
+            validKeys[idx++] = i;
+        }
+
+        // Test all valid keys
+        for (uint256 i = 0; i < validKeys.length; i++) {
+            uint256 key = validKeys[i];
+            uint256 rate = rates[key];
+            require(rate > 0, string(abi.encodePacked("Rate not found for key: ", vm.toString(key))));
+
+            uint256 bps = dspc.exposed_back(rate);
+            assertEq(bps, key, string(abi.encodePacked("Incorrect BPS conversion for rate index: ", vm.toString(key))));
+        }
+    }
 }

src/test/Rates.sol → src/mocks/RatesMock.sol

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: AGPL-3.0-or-later
 pragma solidity ^0.8.24;
 
-contract Rates {
+contract RatesMock {
     mapping(uint256 => uint256) public rates;
 
     constructor() {