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. td Start description of Savers
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@ScottBob
ScottBob committed Sep 12, 2024
1 parent e8c6abe commit 1e8c345
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44 changes: 44 additions & 0 deletions ...ests-util-tests/src/test/java/com/spun/util/persistence/LoadersAndSaversExamplesTest.java
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
package com.spun.util.persistence;

import com.spun.util.Tuple;
import org.approvaltests.Approvals;
import org.junit.jupiter.api.Test;

Expand Down Expand Up @@ -144,6 +145,48 @@ private DataBase initializeDatabase()
return null;
}
}

class Step4 {
// begin-snippet: step4
public void sendOutSeniorDiscounts(DataBase database, MailServer mailServer)
{
Loader<List<Customer>> seniorCustomerLoader = database::getSeniorCustomers;
sendOutSeniorDiscounts(mailServer, seniorCustomerLoader);
}

public void sendOutSeniorDiscounts(MailServer mailServer, Loader<List<Customer>> seniorCustomerLoader)
{
List<Customer> seniorCustomers = seniorCustomerLoader.load();
for (Customer customer : seniorCustomers)
{
Discount seniorDiscount = getSeniorDiscount();
String message = generateDiscountMessage(customer, seniorDiscount);
mailServer.sendMessage(customer, message);
}
}
// end-snippet
}
class Step4_b {
// begin-snippet: step4_b
public void sendOutSeniorDiscounts(DataBase database, MailServer mailServer)
{
Loader<List<Customer>> seniorCustomerLoader = database::getSeniorCustomers;
Saver<Tuple<Customer, String>> mailSaver = Saver2.create(mailServer::sendMessage);
sendOutSeniorDiscounts(mailSaver, seniorCustomerLoader);
}

public void sendOutSeniorDiscounts(Saver<Tuple<Customer, String>> mailSaver, Loader<List<Customer>> seniorCustomerLoader)
{
List<Customer> seniorCustomers = seniorCustomerLoader.load();
for (Customer customer : seniorCustomers)
{
Discount seniorDiscount = getSeniorDiscount();
String message = generateDiscountMessage(customer, seniorDiscount);
mailSaver.save(new Tuple(customer, message));
}
}
// end-snippet
}
private String generateDiscountMessage(Customer customer, Discount seniorDiscount)
{
return null;
Expand Down Expand Up @@ -185,4 +228,5 @@ public String toString()
private class Discount
{
}

}
123 changes: 56 additions & 67 deletions approvaltests-util/docs/how_to/LoadersAndSavers.md
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Original file line number Diff line number Diff line change
Expand Up @@ -170,7 +170,7 @@ Step 5: Now we introduce the new loader function as a parameter to the original

Step 6: Update the unit tests to use the new Loader parameter.
We have now removed the reliance on the database to retrieve the data.
We still rely on a mail server to send the results.
Note that we still rely on a mail server to send the results.

<!-- Snippet Compare: step0, step0_b -->

Expand All @@ -197,72 +197,61 @@ We still rely on a mail server to send the results.
}
</pre>


Step 7: Now we can remove the DataBase as a parameter altogether.

public void sendOutSeniorDiscounts(DataBase database, MailServer mailServer, Loader&lt;List<Customer&gt;> seniorCustomerLoader) {

&nbsp; List seniorCustomers = seniorCustomerLoader.load();

&nbsp; // ...

}

becomes

public void sendOutSeniorDiscounts(MailServer, Loader&lt;List<Customer&gt;> seniorCustomerLoader) { ... }

and we can now remove that parameter from any function that calls this one - including our test.
And we can now remove that parameter from any function that calls this one - including our test.

This removes the dependency on the database for testing purposes.

Why not just use a mock object to do this?

Because mocking the object in question may require much more than what we are doing here. In this case we are simply replacing a call to a method with the result of that method - as if it were called. Defining a mock object would require more overhead and initialization.
Because mocking the object in question may require much more than what we are doing here.
In this case we are simply replacing a call to a method with the result of that method - as if it were called.
Defining a mock object would require much more overhead and initialization.

But we still have a dependency on the MailServer in the example above.

Thanks for pointing that out! We'll now show how to solve that problem using a Saver.

Savers
## Savers

Let's continue with the above example:

public void sendOutSeniorDiscounts(MailServer mailServer, Loader&lt;List<Customer&gt;> seniorCustomerLoader) {

&nbsp; List seniorCustomers = seniorCustomerLoader.load();

&nbsp; for (Customer customer : seniorCustomers) {

&nbsp; Discount seniorDiscount = getSeniorDiscount();

&nbsp; String message = generateDiscountMessage(customer, seniorDiscount);

&nbsp; mailServer.sendMessage(customer, message);

&nbsp; }

<!-- Snippet: step4 -->
```java
public void sendOutSeniorDiscounts(DataBase database, MailServer mailServer)
{
Loader<List<Customer>> seniorCustomerLoader = database::getSeniorCustomers;
sendOutSeniorDiscounts(mailServer, seniorCustomerLoader);
}

public void sendOutSeniorDiscounts(MailServer mailServer, Loader<List<Customer>> seniorCustomerLoader)
{
List<Customer> seniorCustomers = seniorCustomerLoader.load();
for (Customer customer : seniorCustomers)
{
Discount seniorDiscount = getSeniorDiscount();
String message = generateDiscountMessage(customer, seniorDiscount);
mailServer.sendMessage(customer, message);
}
}
```
Here we're sending out an email message. But we don't really care if it gets sent, we just want to make sure it contains the information we expect. Replacing the MailServer object with a Saver is very similar to the process of introducing a Loader.

Step 1: Determine the function that we call to save (or in this case, send) the data.

public void sendOutSeniorDiscounts(MailServer mailServer, Loader&lt;List<Customer&gt;> seniorCustomerLoader) {

&nbsp; List seniorCustomers = seniorCustomerLoader.load();
List seniorCustomers = seniorCustomerLoader.load();

&nbsp; for (Customer customer : seniorCustomers) {
for (Customer customer : seniorCustomers) {

&nbsp; Discount seniorDiscount = getSeniorDiscount();
Discount seniorDiscount = getSeniorDiscount();

&nbsp; String message = generateDiscountMessage(customer, seniorDiscount);
String message = generateDiscountMessage(customer, seniorDiscount);

&nbsp; **mailServer.sendMessage(new Email(customer, message));**
**mailServer.sendMessage(new Email(customer, message));**

**mailSaver.save(new Email(customer, message));**

&nbsp; }
}

Record Email(Customer customer, String message) {}

Expand All @@ -274,39 +263,39 @@ public void senior_customer_message_indicates_benefits_for_those_over_age_65() {

Stack&lt;Email&gt; sent = new Stack<>();

&nbsp; List seniorCustomers = List.of(new Customer("Bob", "Jones", /\* ... /), / ... \*/);
List seniorCustomers = List.of(new Customer("Bob", "Jones", /\* ... /), / ... \*/);

&nbsp; sendOutSeniorDiscounts(null, m -> sent.push(m), () -> seniorCustomers));
sendOutSeniorDiscounts(null, m -> sent.push(m), () -> seniorCustomers));

&nbsp; Approvals.verifyAll(“Email”, sent);
Approvals.verifyAll(“Email”, sent);

}

Step 3: In the test, replace the object that does the saving with a Saver.

public void senior_customer_message_indicates_benefits_for_those_over_age_65() {

&nbsp; TestMailServer mailServer = new TestMailServer();
TestMailServer mailServer = new TestMailServer();

&nbsp; List seniorCustomers = List.of(new Customer("Bob", "Jones", /\* ... /), / ... \*/);
List seniorCustomers = List.of(new Customer("Bob", "Jones", /\* ... /), / ... \*/);

&nbsp; sendOutSeniorDiscounts(null, () -> mailServer, () -> seniorCustomers));
sendOutSeniorDiscounts(null, () -> mailServer, () -> seniorCustomers));

&nbsp; Approvals.verifyAll(mailServer.getMessage());
Approvals.verifyAll(mailServer.getMessage());

}

Class TestMailServer() {

&nbsp; private String message;
private String message;

&nbsp; void sendMessage(Customer customer, String message) {
void sendMessage(Customer customer, String message) {

&nbsp; this.message = message;
this.message = message;

&nbsp; }
}

&nbsp; String getMessage() { return message; }
String getMessage() { return message; }

}

Expand All @@ -324,49 +313,49 @@ Step 5: Now we introduce the new saver function as a parameter to the original f

public void sendOutSeniorDiscounts(MailServer mailServer, Loader&lt;List&gt; seniorCustomerLoader) {

&nbsp; // ...
// ...

&nbsp; ((Saver&lt;MailServer&gt;)() -> mailServer.sendMessage(customer, message)).save();
((Saver&lt;MailServer&gt;)() -> mailServer.sendMessage(customer, message)).save();

&nbsp; // ...
// ...

}

becomes

public void sendOutSeniorDiscounts(MailServer mailServer, Saver&lt;MailServer&gt; mailServerSaver, Loader&lt;List&gt; seniorCustomerLoader) {

&nbsp; // ...
// ...

&nbsp; mailServerSaver.save();
mailServerSaver.save();

&nbsp; // ...
// ...

}

Step 6: Update the calls to this function to use the new Saver parameter.

public void senior_customer_list_includes_only_those_over_age_65() {

&nbsp; TestMailServer mailServer = new TestMailServer();
TestMailServer mailServer = new TestMailServer();

&nbsp; List seniorCustomers = List.of(new Customer("Bob", "Jones", /\* ... /), / ... \*/);
List seniorCustomers = List.of(new Customer("Bob", "Jones", /\* ... /), / ... \*/);

&nbsp; sendOutSeniorDiscounts(null, () -> mailServer, () -> seniorCustomers));
sendOutSeniorDiscounts(null, () -> mailServer, () -> seniorCustomers));

&nbsp; Approvals.verifyAll(mailServer.getRecipients());
Approvals.verifyAll(mailServer.getRecipients());

}

Step 7: Now we can remove the MailServer as a parameter altogether.

public void sendOutSeniorDiscounts(MailServer mailServer, Saver&lt;MailServer&gt; mailServerSaver, Loader&lt;List&gt; seniorCustomerLoader) {

&nbsp; // ...
// ...

&nbsp; mailServerSaver.save();
mailServerSaver.save();

&nbsp; // ...
// ...

}

Expand All @@ -378,6 +367,6 @@ and we can now remove that parameter from any function that calls this one - inc

This removes the dependency on the MailServer for testing purposes.

&nbsp;

&nbsp;


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