@Shreyas165 Thanks for reporting.

Could you update issue description to follow the format of issue template? At least, I need to know the context information about your operating system, terminal emulator and the revision of go-prompt.
https://github.com/c-bata/go-prompt/blob/master/.github/ISSUE_TEMPLATE.md

Operating System: Mac OS 10.13
Terminal Emulator: (i.e. iTerm2) : This issue was not reproduced using terminal, It was a TestCase evaluation.
tag of go-prompt or commit revision: pulled the lastest master 63e3a6f

The sample test case which was used when the issue occurred :
func TestCLIPrompt_Completer(t *testing.T) {
buffer := goPrompt.NewBuffer()
buffer.InsertText("one", true, true) // this results in the panic
fmt.Println(buffer.Document())
buffer.CursorRight(2)
fmt.Println(buffer.Document())
}

run the above test in a golang editor or probably gotest will result in the above mentioned panic

Thanks. Could you rewrite the issue description in following format?
https://github.com/c-bata/go-prompt/blob/master/.github/ISSUE_TEMPLATE.md

@c-bata I fixed a similar issue using:

**--- a/vendor/github.com/c-bata/go-prompt/completion.go
+++ b/vendor/github.com/c-bata/go-prompt/completion.go
@@ -41,7 +41,7 @@ type CompletionManager struct {
 
 // GetSelectedSuggestion returns the selected item.
 func (c *CompletionManager) GetSelectedSuggestion() (s Suggest, ok bool) {
-       if c.selected == -1 {
+       if c.selected == -1 || len(c.tmp) < 1 {
                return Suggest{}, false

I am getting the same error when trying to bind a Shortcut key to insert text into the prompt buffer.
OS: Mojave 10.14.1
Terminal: OSX Terminal Version 2.9.1

// this works but clears the terminal
buf.InsertText("test string", false, true)

// this fails with "panic: runtime error: slice bounds out of range"
buf.InsertText("test string", true, true)