I have need test class for this...............................

public class pkbCaseHistoriesComponentController {

public Id caseId {get; set;}
public cHistories[] histories;

// Variables
public Static final Map<String, Schema.SObjectField> CaseFieldmap = Schema.SObjectType.Case.fields.getMap();
public Static final List<Schema.PicklistEntry> fieldPicklistValues = CaseHistory.Field.getDescribe().getPicklistValues();

public List<cHistories> getHistories()
{
list<cHistories> histories = new list<cHistories>();
String prevDate = '';
for(CaseHistory cHistory : [Select CreatedDate, CreatedBy.Name, CreatedBy.Id, Field, NewValue, OldValue from CaseHistory where CaseId = :caseId order by CreatedDate desc])
{
if((cHistory.newValue == null && cHistory.oldValue == null)
|| (cHistory.newValue != null && !(string.valueOf(cHistory.newValue).startsWith('005') || string.valueOf(cHistory.newValue).startsWith('00G')))
|| (cHistory.oldValue != null && !(string.valueOf(cHistory.oldValue).startsWith('005') || string.valueOf(cHistory.oldValue).startsWith('00G'))))
{
cHistories tempHistory = new cHistories();
// Set the Date and who performed the action
if(String.valueOf(cHistory.CreatedDate) != prevDate){
tempHistory.theDate = String.valueOf(cHistory.CreatedDate);
tempHistory.who = cHistory.CreatedBy.Name;
tempHistory.userId = cHistory.CreatedBy.Id;
}
else
{
tempHistory.theDate = '';
tempHistory.who = '';
tempHistory.userId = cHistory.CreatedBy.Id;
}
prevDate = String.valueOf(cHistory.CreatedDate);

// Get the field label
String fieldLabel = pkbCaseHistoriesComponentController.returnFieldLabel(String.valueOf(cHistory.Field));

// Set the Action value
if (String.valueOf(cHistory.Field) == 'created') { // on Creation
tempHistory.action = 'Created.';
}
else if(cHistory.OldValue != null && cHistory.NewValue == null){ // when deleting a value from a field
// Format the Date and if there's an error, catch it and re
try {
tempHistory.action = 'Deleted ' + Date.valueOf(cHistory.OldValue).format() + ' in <b>' + fieldLabel + '</b>.';
} catch (Exception e){
tempHistory.action = 'Deleted ' + String.valueOf(cHistory.OldValue) + ' in <b>' + fieldLabel + '</b>.';
}
}
else{ // all other scenarios
String fromText = '';
if (cHistory.OldValue != null) {
try {
fromText = ' from ' + Date.valueOf(cHistory.OldValue).format();
} catch (Exception e) {
fromText = ' from ' + String.valueOf(cHistory.OldValue);
}
}

String toText = '';
if (cHistory.OldValue != null) {
try {
toText = Date.valueOf(cHistory.NewValue).format();
} catch (Exception e) {
toText = String.valueOf(cHistory.NewValue);
}
}
if(toText != '')
tempHistory.action = 'Changed <b>' + fieldLabel + '</b>' + fromText + ' to <b>' + toText + '</b>.';
else
tempHistory.action = 'Changed <b>' + fieldLabel;
}

// Add to the list
histories.add(tempHistory);
}
}

return histories;
}

// Function to return Field Label of a Case field given a Field API name
public Static String returnFieldLabel(String fieldName)
{
if(pkbCaseHistoriesComponentController.CaseFieldmap.containsKey(fieldName))
return pkbCaseHistoriesComponentController.CaseFieldmap.get(fieldName).getDescribe().getLabel();
else
{
for(Schema.PicklistEntry pickList : fieldPicklistValues)
{
if(pickList.getValue() == fieldName)
{
if(pickList.getLabel() != null)
return pickList.getLabel();
else
return pickList.getValue();
}
}
}
return '';
}
// Inner Class to store the detail of the case histories
public class cHistories {

public String theDate {get; set;}
public String who {get; set;}
public Id userId {get; set;}
public String action {get; set;}
}
}