add op.Result function, add op tests

op/op.go

@@ -162,3 +162,11 @@ func Identity[T any](v T) func() T {
 		return v
 	}
 }
+
+// Result returns err if it is not nil, otherwise it returns value.
+func Result(err error, value any) any {
+	if err != nil {
+		return err
+	}
+	return value
+}

op/op_test.go

@@ -240,6 +240,109 @@ func TestAddr(t *testing.T) {
 	}
 }
 
+func TestMust(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Errorf("Must did not panic")
+		}
+	}()
+	op.Must(fmt.Errorf("error"))
+}
+
+func TestMustValue(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Errorf("Must did not panic")
+		}
+	}()
+	op.MustValue(42, fmt.Errorf("error"))
+}
+
+func TestMustValue_no_panic(t *testing.T) {
+	if got := op.MustValue(42, nil); got != 42 {
+		t.Errorf("MustValue(42, nil) = %v, want 42", got)
+	}
+}
+
+func TestReverseCompare(t *testing.T) {
+	cmp := func(x, y int) int {
+		if x < y {
+			return -1
+		}
+		if x > y {
+			return 1
+		}
+		return 0
+	}
+	revCmp := op.ReverseCompare(cmp)
+
+	if got := revCmp(1, 2); got != 1 {
+		t.Errorf("ReverseCompare(cmp)(1, 2) = %v, want 1", got)
+	}
+	if got := revCmp(2, 1); got != -1 {
+		t.Errorf("ReverseCompare(cmp)(2, 1) = %v, want -1", got)
+	}
+	if got := revCmp(1, 1); got != 0 {
+		t.Errorf("ReverseCompare(cmp)(1, 1) = %v, want 0", got)
+	}
+}
+
+func TestZero(t *testing.T) {
+	if zero := op.Zero[bool](); zero != false {
+		t.Errorf("Zero[bool]() = %v, want false", zero)
+	}
+	if zero := op.Zero[int](); zero != 0 {
+		t.Errorf("Zero[int]() = %v, want 0", zero)
+	}
+	if zero := op.Zero[string](); zero != "" {
+		t.Errorf("Zero[string]() = %v, want \"\"", zero)
+	}
+	if zero := op.Zero[float64](); zero != 0.0 {
+		t.Errorf("Zero[float64]() = %v, want 0.0", zero)
+	}
+	if zero := op.Zero[error](); zero != nil {
+		t.Errorf("Zero[error]() = %v, want nil", zero)
+	}
+}
+
+func TestIdentity(t *testing.T) {
+	x := 42
+	if got := op.Identity(x)(); got != x {
+		t.Errorf("Identity(%v)() = %v, want %v", x, got, x)
+	}
+	e := fmt.Errorf("error")
+	if got := op.Identity(e)(); got != e {
+		t.Errorf("Identity(%v)() = %v, want %v", e, got, e)
+	}
+}
+
+func TestResult(t *testing.T) {
+	var err = fmt.Errorf("error")
+	tests := []struct {
+		name string
+		a    error
+		b    any
+		want any
+	}{
+		{"nil", nil, 1, 1},
+		{"error", err, 1, err},
+		{"nil_nil", nil, nil, nil},
+		{"error_nil", err, nil, err},
+		{"nil_error", nil, err, err},
+		{"nil_string", nil, "string", "string"},
+		{"error_string", err, "string", err},
+		{"nil_float", nil, 1.0, 1.0},
+		{"error_float", err, 1.0, err},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := op.Result(tt.a, tt.b); got != tt.want {
+				t.Errorf("Result(%v, %v) = %v, want %v", tt.a, tt.b, got, tt.want)
+			}
+		})
+	}
+}
+
 func ExampleOr() {
 	fmt.Println(op.Or(0, 1))
 	fmt.Println(op.Or(2, 3))