Added unit testing for astformat (#473)

* Added unit testing for PostgresSelectExprsFormatting and astformat.String. Very sparse coverage for PostgresSelectExprsFormatting since I couldn't find a constructor for the ColIdent, ColName, and other SQLNode types.

* Fixed linting issues

internal/stackql/astformat/ast_format_test.go

@@ -0,0 +1,97 @@
+package astformat //nolint:testpackage // don't use an underscore in package name
+
+import (
+	"testing"
+
+	"github.com/stackql/stackql-parser/go/vt/sqlparser"
+	"github.com/stackql/stackql/internal/stackql/parser"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// sqlNodes are used for both.
+//
+//nolint:gochecknoglobals // allows test functions to share test cases, only used by ast_format_test, unique names
+var astFormatTestselectNode, astFormatTestdropNode sqlparser.Statement
+
+func TestMain(m *testing.M) {
+	p, _ := parser.NewParser()
+	astFormatTestselectNode, _ = p.ParseQuery("select 1+2*3 from a WHERE a.v1 = 3")
+	astFormatTestdropNode, _ = p.ParseQuery("DROP TABLE tab")
+	m.Run()
+}
+
+func TestPostgresSelectExprsFormatter(t *testing.T) {
+	// only covers SELECT and DROP Statements.
+	// Doesn't cover most actual SQL Nodes.
+	// no constructor for ColName, ColIdent, ...
+	selNode, ok1 := astFormatTestselectNode.(sqlparser.SQLNode)
+	droNode, ok2 := astFormatTestdropNode.(sqlparser.SQLNode)
+	if !ok1 || !ok2 {
+		t.Errorf("selectNode and/or dropNode are not of type sqlparser.SQLNode")
+		return
+	}
+	tests := []struct {
+		name     string
+		node     sqlparser.SQLNode
+		expected string
+	}{
+		{
+			"PostgresSelectExprsFormatter: select",
+			selNode,
+			"select 1 + 2 * 3 from \"a\" where \"a\".v1 = 3",
+		},
+		{
+			"PostgresSelectExprsFormatter: drop",
+			droNode,
+			"drop table \"tab\"",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			buf := sqlparser.NewTrackedBuffer(nil)
+
+			PostgresSelectExprsFormatter(buf, tt.node)
+
+			// assert.Equal(t, fmt.Sprintf("TYPE: %T\n",tt.node), "").
+			switch tt.node.(type) { //nolint:gocritic // switch makes it easily extendable in case we want to add more test cases
+			case *sqlparser.GroupConcatExpr:
+				assert.Equal(t, true, false)
+			}
+			assert.Equal(t, tt.expected, buf.String())
+		})
+	}
+}
+
+func TestString(t *testing.T) {
+	selNode, ok1 := astFormatTestselectNode.(sqlparser.SQLNode)
+	droNode, ok2 := astFormatTestdropNode.(sqlparser.SQLNode)
+	if !ok1 || !ok2 {
+		t.Errorf("selectNode and/or dropNode are not of type sqlparser.SQLNode")
+		return
+	}
+
+	tests := []struct {
+		name     string
+		node     sqlparser.SQLNode
+		expected string
+	}{
+		{
+			"string: select query",
+			selNode,
+			"select 1 + 2 * 3 from \"a\" where \"a\".\"v1\" = 3",
+		},
+		{
+			"string: drop query",
+			droNode,
+			"drop table \"tab\"",
+		},
+	}
+	var formatter sqlparser.NodeFormatter = PostgresSelectExprsFormatter
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := String(tt.node, formatter)
+			assert.Equal(t, tt.expected, got)
+		})
+	}
+}