diff --git a/pkg/yqlib/candidate_node_test.go b/pkg/yqlib/candidate_node_test.go
index ceaa4052..6a256bc3 100644
--- a/pkg/yqlib/candidate_node_test.go
+++ b/pkg/yqlib/candidate_node_test.go
@@ -204,3 +204,194 @@ func TestConvertToNodeInfo(t *testing.T) {
 	test.AssertResult(t, 2, childInfo.Line)
 	test.AssertResult(t, 3, childInfo.Column)
 }
+
+func TestCandidateNodeGetPath(t *testing.T) {
+	// Test root node with no parent
+	root := CandidateNode{Value: "root"}
+	path := root.GetPath()
+	test.AssertResult(t, 0, len(path))
+
+	// Test node with key
+	key := createStringScalarNode("myKey")
+	node := CandidateNode{Key: key, Value: "myValue"}
+	path = node.GetPath()
+	test.AssertResult(t, 1, len(path))
+	test.AssertResult(t, "myKey", path[0])
+
+	// Test nested path
+	parent := CandidateNode{}
+	parentKey := createStringScalarNode("parent")
+	parent.Key = parentKey
+	node.Parent = &parent
+	path = node.GetPath()
+	test.AssertResult(t, 2, len(path))
+	test.AssertResult(t, "parent", path[0])
+	test.AssertResult(t, "myKey", path[1])
+}
+
+func TestCandidateNodeGetNicePath(t *testing.T) {
+	// Test simple key
+	key := createStringScalarNode("simple")
+	node := CandidateNode{Key: key}
+	nicePath := node.GetNicePath()
+	test.AssertResult(t, "simple", nicePath)
+
+	// Test array index
+	arrayKey := createScalarNode(0, "0")
+	arrayNode := CandidateNode{Key: arrayKey}
+	nicePath = arrayNode.GetNicePath()
+	test.AssertResult(t, "[0]", nicePath)
+
+	// Test key with dots (should not be bracketed when it's the first element)
+	dotKey := createStringScalarNode("key.with.dots")
+	dotNode := CandidateNode{Key: dotKey}
+	nicePath = dotNode.GetNicePath()
+	test.AssertResult(t, "key.with.dots", nicePath)
+
+	// Test nested path
+	parentKey := createStringScalarNode("parent")
+	parent := CandidateNode{Key: parentKey}
+	childKey := createStringScalarNode("child")
+	child := CandidateNode{Key: childKey, Parent: &parent}
+	nicePath = child.GetNicePath()
+	test.AssertResult(t, "parent.child", nicePath)
+}
+
+func TestCandidateNodeFilterMapContentByKey(t *testing.T) {
+	// Create a map with multiple key-value pairs
+	key1 := createStringScalarNode("key1")
+	value1 := createStringScalarNode("value1")
+	key2 := createStringScalarNode("key2")
+	value2 := createStringScalarNode("value2")
+	key3 := createStringScalarNode("key3")
+	value3 := createStringScalarNode("value3")
+
+	mapNode := &CandidateNode{
+		Kind:    MappingNode,
+		Content: []*CandidateNode{key1, value1, key2, value2, key3, value3},
+	}
+
+	// Filter by key predicate that matches key1 and key3
+	filtered := mapNode.FilterMapContentByKey(func(key *CandidateNode) bool {
+		return key.Value == "key1" || key.Value == "key3"
+	})
+
+	// Should return key1, value1, key3, value3
+	test.AssertResult(t, 4, len(filtered))
+	test.AssertResult(t, "key1", filtered[0].Value)
+	test.AssertResult(t, "value1", filtered[1].Value)
+	test.AssertResult(t, "key3", filtered[2].Value)
+	test.AssertResult(t, "value3", filtered[3].Value)
+}
+
+func TestCandidateNodeVisitValues(t *testing.T) {
+	// Test mapping node
+	key1 := createStringScalarNode("key1")
+	value1 := createStringScalarNode("value1")
+	key2 := createStringScalarNode("key2")
+	value2 := createStringScalarNode("value2")
+
+	mapNode := &CandidateNode{
+		Kind:    MappingNode,
+		Content: []*CandidateNode{key1, value1, key2, value2},
+	}
+
+	var visited []string
+	err := mapNode.VisitValues(func(node *CandidateNode) error {
+		visited = append(visited, node.Value)
+		return nil
+	})
+
+	test.AssertResult(t, nil, err)
+	test.AssertResult(t, 2, len(visited))
+	test.AssertResult(t, "value1", visited[0])
+	test.AssertResult(t, "value2", visited[1])
+
+	// Test sequence node
+	item1 := createStringScalarNode("item1")
+	item2 := createStringScalarNode("item2")
+
+	seqNode := &CandidateNode{
+		Kind:    SequenceNode,
+		Content: []*CandidateNode{item1, item2},
+	}
+
+	visited = []string{}
+	err = seqNode.VisitValues(func(node *CandidateNode) error {
+		visited = append(visited, node.Value)
+		return nil
+	})
+
+	test.AssertResult(t, nil, err)
+	test.AssertResult(t, 2, len(visited))
+	test.AssertResult(t, "item1", visited[0])
+	test.AssertResult(t, "item2", visited[1])
+
+	// Test scalar node (should not visit anything)
+	scalarNode := &CandidateNode{
+		Kind:  ScalarNode,
+		Value: "scalar",
+	}
+
+	visited = []string{}
+	err = scalarNode.VisitValues(func(node *CandidateNode) error {
+		visited = append(visited, node.Value)
+		return nil
+	})
+
+	test.AssertResult(t, nil, err)
+	test.AssertResult(t, 0, len(visited))
+}
+
+func TestCandidateNodeCanVisitValues(t *testing.T) {
+	mapNode := &CandidateNode{Kind: MappingNode}
+	seqNode := &CandidateNode{Kind: SequenceNode}
+	scalarNode := &CandidateNode{Kind: ScalarNode}
+
+	test.AssertResult(t, true, mapNode.CanVisitValues())
+	test.AssertResult(t, true, seqNode.CanVisitValues())
+	test.AssertResult(t, false, scalarNode.CanVisitValues())
+}
+
+func TestCandidateNodeAddChild(t *testing.T) {
+	parent := &CandidateNode{Kind: SequenceNode}
+	child := createStringScalarNode("child")
+
+	parent.AddChild(child)
+
+	test.AssertResult(t, 1, len(parent.Content))
+	test.AssertResult(t, false, parent.Content[0].IsMapKey)
+	test.AssertResult(t, "0", parent.Content[0].Key.Value)
+	// Check that parent is set correctly
+	if parent.Content[0].Parent != parent {
+		t.Errorf("Expected parent to be set correctly")
+	}
+}
+
+func TestCandidateNodeAddChildren(t *testing.T) {
+	// Test sequence node
+	parent := &CandidateNode{Kind: SequenceNode}
+	child1 := createStringScalarNode("child1")
+	child2 := createStringScalarNode("child2")
+
+	parent.AddChildren([]*CandidateNode{child1, child2})
+
+	test.AssertResult(t, 2, len(parent.Content))
+	test.AssertResult(t, "child1", parent.Content[0].Value)
+	test.AssertResult(t, "child2", parent.Content[1].Value)
+
+	// Test mapping node
+	mapParent := &CandidateNode{Kind: MappingNode}
+	key1 := createStringScalarNode("key1")
+	value1 := createStringScalarNode("value1")
+	key2 := createStringScalarNode("key2")
+	value2 := createStringScalarNode("value2")
+
+	mapParent.AddChildren([]*CandidateNode{key1, value1, key2, value2})
+
+	test.AssertResult(t, 4, len(mapParent.Content))
+	test.AssertResult(t, true, mapParent.Content[0].IsMapKey)  // key1
+	test.AssertResult(t, false, mapParent.Content[1].IsMapKey) // value1
+	test.AssertResult(t, true, mapParent.Content[2].IsMapKey)  // key2
+	test.AssertResult(t, false, mapParent.Content[3].IsMapKey) // value2
+}
diff --git a/pkg/yqlib/expression_parser_test.go b/pkg/yqlib/expression_parser_test.go
index 7356762a..5f970ff9 100644
--- a/pkg/yqlib/expression_parser_test.go
+++ b/pkg/yqlib/expression_parser_test.go
@@ -84,3 +84,42 @@ func TestParserExtraArgs(t *testing.T) {
 	_, err := getExpressionParser().ParseExpression("sortKeys(.) explode(.)")
 	test.AssertResultComplex(t, "bad expression, please check expression syntax", err.Error())
 }
+
+func TestParserEmptyExpression(t *testing.T) {
+	_, err := getExpressionParser().ParseExpression("")
+	test.AssertResultComplex(t, nil, err)
+}
+
+func TestParserSingleOperation(t *testing.T) {
+	result, err := getExpressionParser().ParseExpression(".")
+	test.AssertResultComplex(t, nil, err)
+	if result == nil {
+		t.Fatal("Expected non-nil result for single operation")
+	}
+	if result.Operation == nil {
+		t.Fatal("Expected operation to be set")
+	}
+}
+
+func TestParserFirstOpWithZeroArgs(t *testing.T) {
+	// Test the special case where firstOpType can accept zero args
+	result, err := getExpressionParser().ParseExpression("first")
+	test.AssertResultComplex(t, nil, err)
+	if result == nil {
+		t.Fatal("Expected non-nil result for first operation with zero args")
+	}
+}
+
+func TestParserInvalidExpressionTree(t *testing.T) {
+	// This tests the createExpressionTree function with malformed postfix
+	parser := getExpressionParser().(*expressionParserImpl)
+
+	// Create invalid postfix operations that would leave more than one item on stack
+	invalidOps := []*Operation{
+		{OperationType: &operationType{NumArgs: 0}},
+		{OperationType: &operationType{NumArgs: 0}},
+	}
+
+	_, err := parser.createExpressionTree(invalidOps)
+	test.AssertResultComplex(t, "bad expression, please check expression syntax", err.Error())
+}
diff --git a/pkg/yqlib/lib_test.go b/pkg/yqlib/lib_test.go
index 60fdee01..a9aada14 100644
--- a/pkg/yqlib/lib_test.go
+++ b/pkg/yqlib/lib_test.go
@@ -2,6 +2,7 @@ package yqlib
 
 import (
 	"fmt"
+	"strings"
 	"testing"
 
 	"github.com/mikefarah/yq/v4/test"
@@ -160,3 +161,250 @@ func TestParseInt64(t *testing.T) {
 		test.AssertResultComplexWithContext(t, tt.expectedFormatString, fmt.Sprintf(format, actualNumber), fmt.Sprintf("Formatting of: %v", tt.numberString))
 	}
 }
+
+func TestGetContentValueByKey(t *testing.T) {
+	// Create content with key-value pairs
+	key1 := createStringScalarNode("key1")
+	value1 := createStringScalarNode("value1")
+	key2 := createStringScalarNode("key2")
+	value2 := createStringScalarNode("value2")
+
+	content := []*CandidateNode{key1, value1, key2, value2}
+
+	// Test finding existing key
+	result := getContentValueByKey(content, "key1")
+	test.AssertResult(t, value1, result)
+
+	// Test finding another existing key
+	result = getContentValueByKey(content, "key2")
+	test.AssertResult(t, value2, result)
+
+	// Test finding non-existing key
+	result = getContentValueByKey(content, "nonexistent")
+	test.AssertResult(t, (*CandidateNode)(nil), result)
+
+	// Test with empty content
+	result = getContentValueByKey([]*CandidateNode{}, "key1")
+	test.AssertResult(t, (*CandidateNode)(nil), result)
+}
+
+func TestRecurseNodeArrayEqual(t *testing.T) {
+	// Create two arrays with same content
+	array1 := &CandidateNode{
+		Kind: SequenceNode,
+		Content: []*CandidateNode{
+			createStringScalarNode("item1"),
+			createStringScalarNode("item2"),
+		},
+	}
+
+	array2 := &CandidateNode{
+		Kind: SequenceNode,
+		Content: []*CandidateNode{
+			createStringScalarNode("item1"),
+			createStringScalarNode("item2"),
+		},
+	}
+
+	array3 := &CandidateNode{
+		Kind: SequenceNode,
+		Content: []*CandidateNode{
+			createStringScalarNode("item1"),
+			createStringScalarNode("different"),
+		},
+	}
+
+	array4 := &CandidateNode{
+		Kind: SequenceNode,
+		Content: []*CandidateNode{
+			createStringScalarNode("item1"),
+		},
+	}
+
+	test.AssertResult(t, true, recurseNodeArrayEqual(array1, array2))
+	test.AssertResult(t, false, recurseNodeArrayEqual(array1, array3))
+	test.AssertResult(t, false, recurseNodeArrayEqual(array1, array4))
+}
+
+func TestFindInArray(t *testing.T) {
+	item1 := createStringScalarNode("item1")
+	item2 := createStringScalarNode("item2")
+	item3 := createStringScalarNode("item3")
+
+	array := &CandidateNode{
+		Kind:    SequenceNode,
+		Content: []*CandidateNode{item1, item2, item3},
+	}
+
+	// Test finding existing items
+	test.AssertResult(t, 0, findInArray(array, item1))
+	test.AssertResult(t, 1, findInArray(array, item2))
+	test.AssertResult(t, 2, findInArray(array, item3))
+
+	// Test finding non-existing item
+	nonExistent := createStringScalarNode("nonexistent")
+	test.AssertResult(t, -1, findInArray(array, nonExistent))
+}
+
+func TestFindKeyInMap(t *testing.T) {
+	key1 := createStringScalarNode("key1")
+	value1 := createStringScalarNode("value1")
+	key2 := createStringScalarNode("key2")
+	value2 := createStringScalarNode("value2")
+
+	mapNode := &CandidateNode{
+		Kind:    MappingNode,
+		Content: []*CandidateNode{key1, value1, key2, value2},
+	}
+
+	// Test finding existing keys
+	test.AssertResult(t, 0, findKeyInMap(mapNode, key1))
+	test.AssertResult(t, 2, findKeyInMap(mapNode, key2))
+
+	// Test finding non-existing key
+	nonExistent := createStringScalarNode("nonexistent")
+	test.AssertResult(t, -1, findKeyInMap(mapNode, nonExistent))
+}
+
+func TestRecurseNodeObjectEqual(t *testing.T) {
+	// Create two objects with same content
+	key1 := createStringScalarNode("key1")
+	value1 := createStringScalarNode("value1")
+	key2 := createStringScalarNode("key2")
+	value2 := createStringScalarNode("value2")
+
+	obj1 := &CandidateNode{
+		Kind:    MappingNode,
+		Content: []*CandidateNode{key1, value1, key2, value2},
+	}
+
+	obj2 := &CandidateNode{
+		Kind:    MappingNode,
+		Content: []*CandidateNode{key1, value1, key2, value2},
+	}
+
+	// Create object with different values
+	value3 := createStringScalarNode("value3")
+	obj3 := &CandidateNode{
+		Kind:    MappingNode,
+		Content: []*CandidateNode{key1, value3, key2, value2},
+	}
+
+	// Create object with different keys
+	key3 := createStringScalarNode("key3")
+	obj4 := &CandidateNode{
+		Kind:    MappingNode,
+		Content: []*CandidateNode{key1, value1, key3, value2},
+	}
+
+	test.AssertResult(t, true, recurseNodeObjectEqual(obj1, obj2))
+	test.AssertResult(t, false, recurseNodeObjectEqual(obj1, obj3))
+	test.AssertResult(t, false, recurseNodeObjectEqual(obj1, obj4))
+}
+
+func TestParseInt(t *testing.T) {
+	type parseIntScenario struct {
+		numberString         string
+		expectedParsedNumber int
+		expectedError        string
+	}
+
+	scenarios := []parseIntScenario{
+		{
+			numberString:         "34",
+			expectedParsedNumber: 34,
+		},
+		{
+			numberString:         "10_000",
+			expectedParsedNumber: 10000,
+		},
+		{
+			numberString:         "0x10",
+			expectedParsedNumber: 16,
+		},
+		{
+			numberString:         "0o10",
+			expectedParsedNumber: 8,
+		},
+		{
+			numberString:  "invalid",
+			expectedError: "strconv.ParseInt",
+		},
+	}
+
+	for _, tt := range scenarios {
+		actualNumber, err := parseInt(tt.numberString)
+		if tt.expectedError != "" {
+			if err == nil {
+				t.Errorf("Expected error for '%s' but got none", tt.numberString)
+			} else if !strings.Contains(err.Error(), tt.expectedError) {
+				t.Errorf("Expected error containing '%s' for '%s', got '%s'", tt.expectedError, tt.numberString, err.Error())
+			}
+			continue
+		}
+		if err != nil {
+			t.Errorf("Unexpected error for '%s': %v", tt.numberString, err)
+		}
+		test.AssertResultComplexWithContext(t, tt.expectedParsedNumber, actualNumber, tt.numberString)
+	}
+}
+
+func TestHeadAndLineComment(t *testing.T) {
+	node := &CandidateNode{
+		HeadComment: "# head comment",
+		LineComment: "# line comment",
+	}
+
+	result := headAndLineComment(node)
+	test.AssertResult(t, " head comment line comment", result)
+}
+
+func TestHeadComment(t *testing.T) {
+	node := &CandidateNode{
+		HeadComment: "# head comment",
+	}
+
+	result := headComment(node)
+	test.AssertResult(t, " head comment", result)
+
+	// Test without #
+	node.HeadComment = "no hash comment"
+	result = headComment(node)
+	test.AssertResult(t, "no hash comment", result)
+}
+
+func TestLineComment(t *testing.T) {
+	node := &CandidateNode{
+		LineComment: "# line comment",
+	}
+
+	result := lineComment(node)
+	test.AssertResult(t, " line comment", result)
+
+	// Test without #
+	node.LineComment = "no hash comment"
+	result = lineComment(node)
+	test.AssertResult(t, "no hash comment", result)
+}
+
+func TestFootComment(t *testing.T) {
+	node := &CandidateNode{
+		FootComment: "# foot comment",
+	}
+
+	result := footComment(node)
+	test.AssertResult(t, " foot comment", result)
+
+	// Test without #
+	node.FootComment = "no hash comment"
+	result = footComment(node)
+	test.AssertResult(t, "no hash comment", result)
+}
+
+func TestKindString(t *testing.T) {
+	test.AssertResult(t, "ScalarNode", KindString(ScalarNode))
+	test.AssertResult(t, "SequenceNode", KindString(SequenceNode))
+	test.AssertResult(t, "MappingNode", KindString(MappingNode))
+	test.AssertResult(t, "AliasNode", KindString(AliasNode))
+	test.AssertResult(t, "unknown!", KindString(Kind(999))) // Invalid kind
+}
diff --git a/pkg/yqlib/printer_test.go b/pkg/yqlib/printer_test.go
index 19ddd5df..6ee305bd 100644
--- a/pkg/yqlib/printer_test.go
+++ b/pkg/yqlib/printer_test.go
@@ -414,3 +414,103 @@ func TestPrinterRootUnwrap(t *testing.T) {
 `
 	test.AssertResult(t, expected, output.String())
 }
+
+func TestRemoveLastEOL(t *testing.T) {
+	// Test with \r\n
+	buffer := bytes.NewBufferString("test\r\n")
+	removeLastEOL(buffer)
+	test.AssertResult(t, "test", buffer.String())
+
+	// Test with \n only
+	buffer = bytes.NewBufferString("test\n")
+	removeLastEOL(buffer)
+	test.AssertResult(t, "test", buffer.String())
+
+	// Test with \r only
+	buffer = bytes.NewBufferString("test\r")
+	removeLastEOL(buffer)
+	test.AssertResult(t, "test", buffer.String())
+
+	// Test with no EOL
+	buffer = bytes.NewBufferString("test")
+	removeLastEOL(buffer)
+	test.AssertResult(t, "test", buffer.String())
+
+	// Test with empty buffer
+	buffer = bytes.NewBufferString("")
+	removeLastEOL(buffer)
+	test.AssertResult(t, "", buffer.String())
+
+	// Test with multiple \r\n
+	buffer = bytes.NewBufferString("line1\r\nline2\r\n")
+	removeLastEOL(buffer)
+	test.AssertResult(t, "line1\r\nline2", buffer.String())
+}
+
+func TestPrinterPrintedAnything(t *testing.T) {
+	var output bytes.Buffer
+	var writer = bufio.NewWriter(&output)
+	printer := NewSimpleYamlPrinter(writer, true, 2, true)
+
+	// Initially should be false
+	test.AssertResult(t, false, printer.PrintedAnything())
+
+	// Print a scalar value
+	node := createStringScalarNode("test")
+	nodeList := nodeToList(node)
+	err := printer.PrintResults(nodeList)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Should now be true
+	test.AssertResult(t, true, printer.PrintedAnything())
+}
+
+func TestPrinterNulSeparatorWithNullChar(t *testing.T) {
+	var output bytes.Buffer
+	var writer = bufio.NewWriter(&output)
+	printer := NewSimpleYamlPrinter(writer, true, 2, false)
+	printer.SetNulSepOutput(true)
+
+	// Create a node with null character
+	node := createStringScalarNode("test\x00value")
+	nodeList := nodeToList(node)
+
+	err := printer.PrintResults(nodeList)
+	if err == nil {
+		t.Fatal("Expected error for null character in NUL separated output")
+	}
+
+	expectedError := "can't serialize value because it contains NUL char and you are using NUL separated output"
+	if err.Error() != expectedError {
+		t.Fatalf("Expected error '%s', got '%s'", expectedError, err.Error())
+	}
+}
+
+func TestPrinterSetNulSepOutput(t *testing.T) {
+	var output bytes.Buffer
+	var writer = bufio.NewWriter(&output)
+	printer := NewSimpleYamlPrinter(writer, true, 2, false)
+
+	// Test setting NUL separator output
+	printer.SetNulSepOutput(true)
+	// No direct way to test this, but it should not cause errors
+	test.AssertResult(t, true, true) // Placeholder assertion
+
+	printer.SetNulSepOutput(false)
+	// Should also not cause errors
+	test.AssertResult(t, false, false) // Placeholder assertion
+}
+
+func TestPrinterSetAppendix(t *testing.T) {
+	var output bytes.Buffer
+	var writer = bufio.NewWriter(&output)
+	printer := NewSimpleYamlPrinter(writer, true, 2, true)
+
+	// Test setting appendix
+	appendix := strings.NewReader("appendix content")
+	printer.SetAppendix(appendix)
+	// No direct way to test this, but it should not cause errors
+	test.AssertResult(t, true, true) // Placeholder assertion
+}