lib/reflect: make the IsNil tests to become an example

In this way we do test and provide an example at the same time.

While at it, add another test cases for boolean, initialized slice, map,
and errors.

2 files changed, 72 insertions, 62 deletions

diff --git a/lib/reflect/reflect_example_test.go b/lib/reflect/reflect_example_test.go
new file mode 100644
index 00000000..41df3727
--- /dev/null
+++ b/lib/reflect/reflect_example_test.go
@@ -0,0 +1,72 @@
+// Copyright 2020, Shulhan <ms@kilabit.info>. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package reflect
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+)
+
+type F func()
+
+type T struct{}
+
+func (t *T) J() bool {
+	return true
+}
+
+func ExampleIsNil() {
+	var (
+		aBoolean   bool
+		aChannel   chan int
+		aFunction  F
+		aMap       map[int]int
+		aPtr       *T
+		aSlice     []int
+		anInt      int
+		emptyError error
+		fs         http.FileSystem
+	)
+
+	cases := []struct {
+		v interface{}
+	}{
+		{}, // Unitialized.
+		{v: aBoolean},
+		{v: aChannel},          // Uninitialized channel.
+		{v: aFunction},         // Empty func type.
+		{v: aMap},              // Unitialized map.
+		{v: make(map[int]int)}, // Initialized map.
+		{v: aPtr},              // Uninitialized pointer to struct.
+		{v: &T{}},              // Initialized pointer to struct.
+		{v: aSlice},            // Unitialized slice.
+		{v: make([]int, 0)},    // Initialized slice.
+		{v: anInt},
+		{v: emptyError},
+		{v: errors.New("e")}, // Initialized error
+		{v: fs},              // Unitialized interface type to interface{}
+	}
+
+	for _, c := range cases {
+		fmt.Printf("%19T: v == nil is %5t, IsNil() is %5t\n", c.v, c.v == nil, IsNil(c.v))
+	}
+
+	//Output:
+	// <nil>: v == nil is  true, IsNil() is  true
+	//                bool: v == nil is false, IsNil() is false
+	//            chan int: v == nil is false, IsNil() is  true
+	//           reflect.F: v == nil is false, IsNil() is  true
+	//         map[int]int: v == nil is false, IsNil() is  true
+	//         map[int]int: v == nil is false, IsNil() is false
+	//          *reflect.T: v == nil is false, IsNil() is  true
+	//          *reflect.T: v == nil is false, IsNil() is false
+	//               []int: v == nil is false, IsNil() is  true
+	//               []int: v == nil is false, IsNil() is false
+	//                 int: v == nil is false, IsNil() is false
+	//               <nil>: v == nil is  true, IsNil() is  true
+	// *errors.errorString: v == nil is false, IsNil() is false
+	//               <nil>: v == nil is  true, IsNil() is  true
+}
diff --git a/lib/reflect/reflect_test.go b/lib/reflect/reflect_test.go
deleted file mode 100644
index 17a41127..00000000
--- a/lib/reflect/reflect_test.go
+++ /dev/null
@@ -1,62 +0,0 @@
-// Copyright 2020, Shulhan <ms@kilabit.info>. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package reflect
-
-import (
-	"net/http"
-	"testing"
-)
-
-type F func()
-
-type T struct{}
-
-func (t *T) J() bool {
-	return true
-}
-
-func TestIsNil(t *testing.T) {
-	var (
-		aChannel  chan int
-		aFunction F
-		aMap      map[int]int
-		aPtr      *T
-		aSlice    []int
-		fs        http.FileSystem
-	)
-
-	cases := []struct {
-		v   interface{}
-		exp bool
-	}{{
-		v: true,
-	}, {
-		v:   aChannel,
-		exp: true,
-	}, {
-		v:   aFunction,
-		exp: true,
-	}, {
-		v:   aMap,
-		exp: true,
-	}, {
-		v:   aPtr,
-		exp: true,
-	}, {
-		v:   aSlice,
-		exp: true,
-	}, {
-		v:   fs,
-		exp: true,
-	}}
-
-	for _, c := range cases {
-		got := IsNil(c.v)
-		if c.exp != got {
-			t.Errorf("Expecting %v, got %v on %v(%T)", c.exp, got,
-				c.v, c.v)
-		}
-	}
-}