Updates repo to forge and adds two new tests.

.gitignore

@@ -1 +1,2 @@
 /out
+/cache

Makefile

@@ -1,5 +1,5 @@
-all     :; DAPP_BUILD_OPTIMIZE=1 DAPP_BUILD_OPTIMIZE_RUNS=200 dapp --use solc:0.6.12 build
-clean   :; dapp clean
-test    :; dapp --use solc:0.6.12 test -v
-deploy  :; make && dapp create LerpFactory
-flatten :; hevm flatten --source-file src/LerpFactory.sol > out/LerpFactory.sol && hevm flatten --source-file src/Lerp.sol > out/Lerp.sol
+all     :; forge build --use solc:0.6.12 --optimize --optimizer-runs 200
+clean   :; forge clean
+test    :; forge test -vvv
+deploy  :; make && forge create LerpFactory
+flatten :; forge flatten --output out/LerpFactory.flattened.sol src/LerpFactory.sol

src/Lerp.t.sol

@@ -117,37 +117,95 @@ contract DssLerpTest is DSTest {
     }
 
     function test_lerp() public {
-        Lerp lerp = new Lerp(address(target), "value", block.timestamp, 1 * TOLL_ONE_PCT, 1 * TOLL_ONE_PCT / 10, 9 days);
+        uint256 startTime = block.timestamp;
+        Lerp lerp = new Lerp(address(target), "value", startTime, 1 * TOLL_ONE_PCT, 1 * TOLL_ONE_PCT / 10, 9 days);
+
         assertEq(lerp.what(), "value");
         assertEq(lerp.start(), 1 * TOLL_ONE_PCT);
         assertEq(lerp.end(), 1 * TOLL_ONE_PCT / 10);
         assertEq(lerp.duration(), 9 days);
         assertTrue(!lerp.done());
-        assertEq(lerp.startTime(), 0);
+        assertEq(lerp.startTime(), block.timestamp);
         assertEq(target.value(), 0);
         target.rely(address(lerp));
         lerp.tick();
         assertTrue(!lerp.done());
         assertEq(lerp.startTime(), block.timestamp);
         assertEq(target.value(), 1 * TOLL_ONE_PCT);
-        hevm.warp(1 days);
+        hevm.warp(startTime + 1 days);
         assertEq(target.value(), 1 * TOLL_ONE_PCT);
         lerp.tick();
         assertEq(target.value(), 9 * TOLL_ONE_PCT / 10);    // 0.9%
-        hevm.warp(2 days);
+        hevm.warp(startTime + 2 days);
         lerp.tick();
         assertEq(target.value(), 8 * TOLL_ONE_PCT / 10);    // 0.8%
-        hevm.warp(2 days + 12 hours);
+        hevm.warp(startTime + 2 days + 12 hours);
         lerp.tick();
         assertEq(target.value(), 75 * TOLL_ONE_PCT / 100);    // 0.75%
-        hevm.warp(12 days);
+        hevm.warp(startTime + 12 days);
         assertEq(target.wards(address(lerp)), 1);
         lerp.tick();
         assertEq(target.value(), 1 * TOLL_ONE_PCT / 10);    // 0.1%
         assertTrue(lerp.done());
         assertEq(target.wards(address(lerp)), 0);
     }
 
+    // Confirm lerp can be used as a durational toggle switch for 0 --> 1 values.
+    function test_lerp_zero_to_one() public {
+        uint256 start = 0;
+        uint256 end = 1;
+        uint256 duration = 30 days;
+        uint256 testStart = block.timestamp;
+
+        Lerp lerp = new Lerp(address(target), "value", testStart, start, end, duration);
+        target.rely(address(lerp));
+        lerp.tick();
+        assertEq(target.value(), 0);
+
+        hevm.warp(testStart + duration/2); // Halfway through
+
+        lerp.tick();
+        assertEq(target.value(), 0);
+
+        hevm.warp(testStart + duration - 1); // One block before completion
+
+        lerp.tick();
+        assertEq(target.value(), 0);
+
+        hevm.warp(testStart + duration);  // End of period
+
+        lerp.tick();
+        assertEq(target.value(), 1);
+    }
+
+    // Confirm lerp can be used as a durational toggle switch for 1 --> 0 values.
+    function test_lerp_one_to_zero() public {
+        uint256 start = 1;
+        uint256 end = 0;
+        uint256 duration = 30 days;
+        uint256 testStart = block.timestamp;
+
+        Lerp lerp = new Lerp(address(target), "value", testStart, start, end, duration);
+        target.rely(address(lerp));
+        lerp.tick();
+        assertEq(target.value(), 1);
+
+        hevm.warp(testStart + duration/2); // Halfway through
+
+        lerp.tick();
+        assertEq(target.value(), 1);
+
+        hevm.warp(testStart + duration - 1); // One block before completion
+
+        lerp.tick();
+        assertEq(target.value(), 1);
+
+        hevm.warp(testStart + duration);  // End of period
+
+        lerp.tick();
+        assertEq(target.value(), 0);
+    }
+
     function test_lerp_max_values1() public {
         uint256 start = 10 ** 59;
         uint256 end = 10 ** 59 - 1;