Fix IntegerArbitrary#shrink to respect min/max bounds

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## [Unreleased]
 
+- Fix `IntegerArbitrary#shrink` to respect min/max bounds [#36](https://github.com/ohbarye/pbt/pull/36)
+
 ## [0.5.0] - 2024-12-30
 
 - [Breaking change] Drop `:process` and `:thread` workers since there are no concrete use cases.

lib/pbt/arbitrary/integer_arbitrary.rb

@@ -20,7 +20,13 @@ def generate(rng)
       end
 
       # @see Arbitrary#shrink
-      def shrink(current, target: DEFAULT_TARGET)
+      def shrink(current, target: nil)
+        # If no target is specified, use the appropriate bound as target
+        target ||= DEFAULT_TARGET.clamp(@min, @max)
+
+        # Ensure target is within bounds
+        target = target.clamp(@min, @max)
+
         gap = current - target
         return Enumerator.new { |_| } if gap == 0
 
@@ -30,9 +36,14 @@ def shrink(current, target: DEFAULT_TARGET)
           while (diff = (current - target).abs) > 1
             halved = diff / 2
             current -= is_positive_gap ? halved : -halved
+            # Ensure current stays within bounds
+            current = current.clamp(@min, @max)
             y.yield current
           end
-          y.yield target # no diff here
+          # Only yield target if it's different from current
+          if current != target
+            y.yield target
+          end
         end
       end
     end

spec/pbt/arbitrary/choose_arbitrary_spec.rb

@@ -27,7 +27,7 @@
 
     it "returns an Enumerator that iterates halved integers towards the min" do
       arb = Pbt::Arbitrary::ChooseArbitrary.new(-2..10)
-      expect(arb.shrink(50).to_a).to eq [24, 11, 5, 2, 0, -1, -2]
+      expect(arb.shrink(50).to_a).to eq [10, 4, 1, 0, -1, -2]
     end
 
     context "when current value and target is same" do

spec/pbt/arbitrary/integer_arbitrary_spec.rb

@@ -53,5 +53,39 @@
         end
       end
     end
+
+    describe "with min/max constraints" do
+      it "shrinks values within the specified range" do
+        arb = Pbt::Arbitrary::IntegerArbitrary.new(25, 65)
+        shrunk_values = arb.shrink(50).to_a
+
+        expect(shrunk_values).to all(be >= 25)
+        expect(shrunk_values).to all(be <= 65)
+      end
+
+      it "shrinks from max value respecting the min constraint" do
+        arb = Pbt::Arbitrary::IntegerArbitrary.new(25, 65)
+        shrunk_values = arb.shrink(65).to_a
+
+        expect(shrunk_values).to all(be >= 25)
+        expect(shrunk_values).to all(be <= 65)
+        expect(shrunk_values.last).to be >= 25
+      end
+
+      it "shrinks from min value respecting the min constraint" do
+        arb = Pbt::Arbitrary::IntegerArbitrary.new(25, 65)
+        shrunk_values = arb.shrink(25).to_a
+
+        expect(shrunk_values).to be_empty
+      end
+
+      it "shrinks negative range values within constraints" do
+        arb = Pbt::Arbitrary::IntegerArbitrary.new(-50, -10)
+        shrunk_values = arb.shrink(-20).to_a
+
+        expect(shrunk_values).to all(be >= -50)
+        expect(shrunk_values).to all(be <= -10)
+      end
+    end
   end
 end