feat: add drop key functionality (#6)

Currently, the `Table.Drop()` function is deprecated because it is not implemented yet. Let's add that functionality.

- Adds true drop functionality to the table, through `Table.Drop()`.
- Adds tests for functionality.
- Rewrites fuzz test using `go_fuzz_utils`, to test arbitrary usage patterns.
- Rewrite `bucket` to allow a capacity of zero.
- Rename `Table.Capacity()` to `Table.TotalCapacity()`, to reflect to different between the capacity of the buckets vs. the whole table.
- Enforce 100% mutation test coverage.

Reviewed-on: #6
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

cuckoo_test.go

@@ -1,6 +1,7 @@
 package cuckoo_test
 
 import (
+	"errors"
 	"maps"
 	"math/rand/v2"
 	"testing"
@@ -64,7 +65,7 @@ func TestStartingCapacity(t *testing.T) {
 	assert := assert.New(t)
 	table := cuckoo.NewTable[int, bool](cuckoo.Capacity(64))
 
-	assert.Equal(uint64(128), table.Capacity())
+	assert.Equal(uint64(128), table.TotalCapacity())
 }
 
 func TestResizeCapacity(t *testing.T) {
@@ -74,12 +75,12 @@ func TestResizeCapacity(t *testing.T) {
 		cuckoo.GrowthFactor(2),
 	)
 
-	for table.Capacity() == 16 {
+	for table.TotalCapacity() == 16 {
 		err := table.Put(rand.Int(), true)
 		assert.NoError(err)
 	}
 
-	assert.Equal(uint64(32), table.Capacity())
+	assert.Equal(uint64(32), table.TotalCapacity())
 }
 
 func TestPutMany(t *testing.T) {
@@ -128,3 +129,113 @@ func TestRemove(t *testing.T) {
 
 	assert.True(table.Has(0))
 }
+
+func TestDropExistingItem(t *testing.T) {
+	assert := assert.New(t)
+	key, value := 0, true
+	table := cuckoo.NewTable[int, bool]()
+	(table.Put(key, value))
+
+	err := table.Drop(key)
+
+	assert.NoError(err)
+	assert.Equal(0, table.Size())
+	assert.False(table.Has(key))
+}
+
+func TestDropNoItem(t *testing.T) {
+	assert := assert.New(t)
+	key := 0
+	table := cuckoo.NewTable[int, bool]()
+
+	err := table.Drop(key)
+
+	assert.NoError(err)
+	assert.Equal(0, table.Size())
+	assert.False(table.Has(key))
+}
+
+func TestDropItemCapacity(t *testing.T) {
+	assert := assert.New(t)
+	key := 0
+	table := cuckoo.NewTable[int, bool](
+		cuckoo.Capacity(64),
+		cuckoo.GrowthFactor(2),
+	)
+
+	startingCapacity := table.TotalCapacity()
+	err := table.Drop(key)
+	endingCapacity := table.TotalCapacity()
+
+	assert.NoError(err)
+	assert.Equal(0, table.Size())
+	assert.Equal(uint64(128), startingCapacity)
+	assert.Equal(uint64(64), endingCapacity)
+}
+
+func TestPutNoCapacity(t *testing.T) {
+	assert := assert.New(t)
+	key, value := 0, true
+	table := cuckoo.NewTable[int, bool](
+		cuckoo.Capacity(0),
+	)
+
+	err := table.Put(key, value)
+
+	assert.NoError(err)
+	assert.Equal(1, table.Size())
+	assert.True(table.Has(key))
+}
+
+func TestBadHashCapacity(t *testing.T) {
+	assert := assert.New(t)
+	table := cuckoo.NewCustomTable[int, bool](
+		func(int) uint64 { return 0 },
+		func(int) uint64 { return 0 },
+		func(a, b int) bool { return a == b },
+		cuckoo.Capacity(20),
+	)
+
+	err1 := table.Put(0, true)
+	err2 := table.Put(1, true)
+	err3 := table.Put(2, true)
+
+	assert.NoError(err1)
+	assert.NoError(err2)
+	assert.Error(err3)
+
+	assert.Equal(uint64(80), table.TotalCapacity())
+}
+
+func TestDropResizeCapacity(t *testing.T) {
+	assert := assert.New(t)
+	table := cuckoo.NewTable[int, bool](
+		cuckoo.Capacity(10),
+	)
+
+	err1 := table.Put(0, true)
+	err2 := table.Put(1, true)
+	err3 := table.Drop(1)
+
+	assert.NoError(errors.Join(err1, err2, err3))
+	assert.Equal(uint64(20), table.TotalCapacity())
+}
+
+func TestNewTableBy(t *testing.T) {
+	type User struct {
+		_    func()
+		id   string
+		name string
+	}
+
+	assert := assert.New(t)
+	table := cuckoo.NewTableBy[User, bool](
+		func(u User) string { return u.id },
+	)
+
+	err := table.Put(User{nil, "1", "Robert"}, true)
+
+	assert.NoError(err)
+	assert.Equal(1, table.Size())
+	assert.True(table.Has(User{nil, "1", "Robbie"}))
+}