fn: Added new slice functions.

Signed-off-by: Ononiwu Maureen <59079323+Chinwendu20@users.noreply.github.com>

fn/slice_test.go

@@ -1,6 +1,7 @@
 package fn
 
 import (
+	"fmt"
 	"slices"
 	"testing"
 
@@ -136,3 +137,107 @@ func TestZipWith(t *testing.T) {
 		z, []bool{false, true, false, false, false},
 	))
 }
+
+// TestSum checks if the Sum function correctly calculates the sum of the
+// numbers in the slice.
+func TestSum(t *testing.T) {
+	tests := []struct {
+		name   string
+		items  interface{}
+		result interface{}
+	}{
+		{
+			name:   "Sum of positive integers",
+			items:  []int{1, 2, 3},
+			result: 6,
+		},
+		{
+			name:   "Sum of negative integers",
+			items:  []int{-1, -2, -3},
+			result: -6,
+		},
+		{
+			name:   "Sum of float numbers",
+			items:  []float64{1.1, 2.2, 3.3},
+			result: 6.6,
+		},
+		{
+			name: "Sum of complex numbers",
+			items: []complex128{
+				complex(1, 1),
+				complex(2, 2),
+				complex(3, 3),
+			},
+			result: complex(6, 6),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			switch v := tt.items.(type) {
+			case []int:
+				require.Equal(t, tt.result, Sum(v))
+			case []float64:
+				require.Equal(t, tt.result, Sum(v))
+			case []complex128:
+				require.Equal(t, tt.result, Sum(v))
+			}
+		})
+	}
+}
+
+// TestSliceToMap tests the SliceToMap function.
+func TestSliceToMap(t *testing.T) {
+	tests := []struct {
+		name      string
+		slice     []int
+		keyFunc   func(int) int
+		valueFunc func(int) string
+		expected  map[int]string
+	}{
+		{
+			name:    "Integers to string map",
+			slice:   []int{1, 2, 3},
+			keyFunc: func(a int) int { return a },
+			valueFunc: func(a int) string {
+				return fmt.Sprintf("Value%d", a)
+			},
+			expected: map[int]string{
+				1: "Value1",
+				2: "Value2",
+				3: "Value3",
+			},
+		},
+		{
+			name:    "Duplicates in slice",
+			slice:   []int{1, 2, 2, 3},
+			keyFunc: func(a int) int { return a },
+			valueFunc: func(a int) string {
+				return fmt.Sprintf("Value%d", a)
+			},
+			expected: map[int]string{
+				1: "Value1",
+				2: "Value2",
+				3: "Value3",
+			},
+		},
+		{
+			name:    "Empty slice",
+			slice:   []int{},
+			keyFunc: func(a int) int { return a },
+			valueFunc: func(a int) string {
+				return fmt.Sprintf("Value%d", a)
+			},
+			expected: map[int]string{},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			require.Equal(
+				t, tt.expected,
+				SliceToMap(tt.slice, tt.keyFunc, tt.valueFunc),
+			)
+		})
+	}
+}