Have --state=closed include merged PRs

Since we currently offer no way of querying PRs by combining multiple
states with an OR, the best way to handle the `closed` state is to match
what the web UI is doing; that is to include merged PRs.

command/pr.go

@@ -163,7 +163,7 @@ func prList(cmd *cobra.Command, args []string) error {
 	case "open":
 		graphqlState = []string{"OPEN"}
 	case "closed":
-		graphqlState = []string{"CLOSED"}
+		graphqlState = []string{"CLOSED", "MERGED"}
 	case "merged":
 		graphqlState = []string{"MERGED"}
 	case "all":

command/pr_test.go

@@ -210,6 +210,30 @@ No pull requests match your search
 	eq(t, reqBody.Variables.Labels, []string{"one", "two", "three"})
 }
 
+func TestPRList_filteringClosed(t *testing.T) {
+	initBlankContext("OWNER/REPO", "master")
+	http := initFakeHTTP()
+	http.StubRepoResponse("OWNER", "REPO")
+
+	respBody := bytes.NewBufferString(`{ "data": {} }`)
+	http.StubResponse(200, respBody)
+
+	_, err := RunCommand(prListCmd, `pr list -s closed`)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	bodyBytes, _ := ioutil.ReadAll(http.Requests[1].Body)
+	reqBody := struct {
+		Variables struct {
+			State []string
+		}
+	}{}
+	json.Unmarshal(bodyBytes, &reqBody)
+
+	eq(t, reqBody.Variables.State, []string{"CLOSED", "MERGED"})
+}
+
 func TestPRList_filteringAssignee(t *testing.T) {
 	initBlankContext("OWNER/REPO", "master")
 	http := initFakeHTTP()