testing examples added

docs/unittesting.md

@@ -30,7 +30,7 @@ Apart from this, Remix allows usage of some special functions to make testing mo
 * `afterEach()` - Runs after each test
 * `afterAll()` - Runs after all tests
 
-To get started, see [this](https://github.com/ethereum/remix/blob/master/remix-tests/tests/examples_4/SafeMath_test.sol) for sample implementation.
+To get started, see [this simple example](./unittesting_examples.html#simple-example).
 
 Run Tests
 ------------------
@@ -39,10 +39,57 @@ Click the button "Run tests" to executes all tests whose box has been checked be
 
 ![](images/a-unit-testing-run-result.png)
 
-Continuous integration
+Customization
+------------------
+Remix facilitates users with various types of customizations to test a contract properly.
+
+**1. Custom Compiler Context**
+
+`Solidity Unit Testing` refers `Solidity Compiler` plugin for compiler configurations. One can provide customized inputs for `Compiler`, `EVM Version` & `Enable Optimization` and these will be the configuration settings used for contract compilation before running unit tests.
+
+![](images/a-unit-testing-custom-compiler-config.png)
+
+**2. Custom Transaction Context**
+
+For a contract method interaction, prime parameters of transaction are `from` address, `value` & `gas`. Usually, we need to test a method's behaviour under different values of these parameters.
+
+Remix provides the functionality of custom `msg.sender` & `msg.value` of transaction using method devdoc like:
+
+```
+/// #sender: account-0
+/// #value: 10
+function checkSenderIs0AndValueis10 () public payable {
+    Assert.equal(msg.sender, TestsAccounts.getAccount(0), "wrong sender in checkSenderIs0AndValueis10");
+    Assert.equal(msg.value, 10, "wrong value in checkSenderIs0AndValueis10");
+}
+```
+Things to keep in mind while using custom transaction context:
+
+1. Parameters must be defined in devdoc of related method
+2. Each parameter key should be prefixed with a hash (**#**) and end with a colon following a space (**: **) like `#sender: ` & `#value: `
+3. For now, customization is available for parameters `sender` & `value` only
+4. Sender is `from` address of a transaction which is accessed using `msg.sender` inside a contract method. It should be defined in a fixed format as '**account-**<account_index>'
+5. `<account_index>` varies from `0-2` before remix-ide release v0.10.0 and `0-9` afterwards
+6. `remix_accounts.sol` must be imported in your test file to use custom `sender`
+7. Value is `value` sent along with a transaction in `wei` which is accessed using `msg.value` inside a contract method. It should be a number.
+
+Regarding `gas`, Remix estimates the required gas for each transaction internally. Still if a contract deployment fails with `Out-of-Gas` error, it tries to redeploy it by doubling the gas. Deployment failing with double gas will show error: ```contract deployment failed after trying twice: The contract code couldn't be stored, please check your gas limit```
+
+Various test examples can be seen in [examples](./unittesting_examples) section.
+
+
+Points to remember
+------------------
+
+* A test contract cannot have a method with parameters. Having one such method will show error: `Method 'methodname' can not have parameters inside a test contract`
+* Number of test accounts are `3` before remix-ide release v0.10.0 and `10` afterwards
+* A test file which imports `remix_accounts.sol` might not compile successfully with `Solidity Compiler` plugin but it will work fine with Solidity Unit Testing plugin.
+
+Remix-tests
 ----------------------
 
-remix-tests is also a CLI, it can be used in a continuous integration environment which support node.js.
-Please find more information in the [remix-tests repository](https://github.com/ethereum/remix/tree/master/remix-tests)
+`remix-tests` is the module which works underneath of remix-ide `Solidity Unit Testing` plugin. 
+
+`remix-tests` is an [NPM package](https://www.npmjs.com/package/remix-tests). It can also be used as  a CLI/CI solution, supporting node.js. Find more information about this type of usage in the [remix-tests repository](https://github.com/ethereum/remix/tree/master/remix-tests#as-command-line-interface)
 
-See also: example [Su Squares contract](https://github.com/su-squares/ethereum-contract/tree/e542f37d4f8f6c7b07d90a6554424268384a4186) and [Travis build](https://travis-ci.org/su-squares/ethereum-contract/builds/446186067) that uses remix-tests for continuous integration testing.
+For CI implementation example, see [Su Squares contract](https://github.com/su-squares/ethereum-contract/tree/e542f37d4f8f6c7b07d90a6554424268384a4186) and [Travis build](https://travis-ci.org/su-squares/ethereum-contract/builds/446186067) that uses `remix-tests` for continuous integration testing.