feat(rule): add string validation rule

* Add 'string' to Validations

* Add test cases for 'string' validations

* Add docs for 'string' schema validation

* fix 'string' skipping test cases

docs/schema-rules.md

@@ -39,6 +39,7 @@ indicative
 - [in](#in)
 - [includes](#includes)
 - [integer](#integer)
+- [string](#string)
 - [ip](#ip)
 - [ipv4](#ipv4)
 - [ipv6](#ipv6)
@@ -234,6 +235,15 @@ the value of field under validation should be an integer
 }
 ```
 
+### string
+the value of field under validation should be a string
+
+```javascript,line-numbers
+{
+  username: 'string'
+}
+```
+
 ### ip
 the value of field under validation should be a valid ip address
 

readme.md

@@ -1356,6 +1356,7 @@ indicative
 [in](#in)
 [includes](#includes)
 [integer](#integer)
+[string](#string)
 [ip](#ip)
 [ipv4](#ipv4)
 [ipv6](#ipv6)
@@ -1553,6 +1554,15 @@ the value of field under validation should be an integer
 }
 ```
 
+#### string
+the value of field under validation should be a string
+
+```javascript
+{
+  username: 'string'
+}
+```
+
 #### ip
 the value of field under validation should be a valid ip address
 

src/Validations/index.js

@@ -1286,6 +1286,33 @@ Validations.regex = function (data, field, message, args, get) {
   })
 }
 
+/**
+ * @description makes sure field under validation is a string
+ * @method regex
+ * @param  {Object} data
+ * @param  {String} field
+ * @param  {String} message
+ * @param  {Array} args
+ * @param  {Function} get
+ * @return {Object}
+ * @public
+ */
+Validations.string = function (data, field, message, args, get) {
+  return new Promise(function (resolve, reject) {
+    const fieldValue = get(data, field)
+    if (skippable(fieldValue)) {
+      resolve('validation skipped')
+      return
+    }
+
+    if (Raw.string(fieldValue)) {
+      resolve('validation passed')
+      return
+    }
+    reject(message)
+  })
+}
+
 /**
  * aliases
  */

test/validations.spec.js

@@ -3106,5 +3106,81 @@ describe('Validations', function() {
       expect(passes).to.equal('validation skipped')
     })
   })
+
+  context('String', function () {
+    ///////////////////
+    // test suite 205 //
+    ///////////////////
+    it('should work fine when the confirmed field is string', function * () {
+      const data = { username: 'david' }
+      const field = 'username'
+      const message = 'Username should be a string'
+      const get = _.get
+      const args = []
+      const passes = yield Validations.string(data, field, message, args, get)
+      expect(passes).to.equal('validation passed')
+    })
+
+    ///////////////////
+    // test suite 206 //
+    ///////////////////
+    it('should throw an error when the confirmed field is a number', function * () {
+      const data = { username: 1234 }
+      const field = 'username'
+      const message = 'Username should be a string'
+      const get = _.get
+      const args = []
+      try {
+        const passes = yield Validations.string(data, field, message, args, get)
+        expect(passes).not.to.exist()
+      } catch(e) {
+        expect(e).to.equal(message)
+      }
+    })
+
+    ///////////////////
+    // test suite 207 //
+    ///////////////////
+    it('should throw an error when the confirmed field is a boolean', function * () {
+      const data = { username: true }
+      const field = 'username'
+      const message = 'Username should be a string'
+      const get = _.get
+      const args = []
+      try {
+        const passes = yield Validations.string(data, field, message, args, get)
+        expect(passes).not.to.exist()
+      } catch(e) {
+        expect(e).to.equal(message)
+      }
+    })
+
+    ///////////////////
+    // test suite 208 //
+    ///////////////////
+    it('should skip validation when field value is not defined', function * () {
+      const data = { }
+      const field = 'username'
+      const message = 'Username should be a string'
+      const get = _.get
+      const args = []
+      const passes = yield Validations.string(data, field, message, args, get)
+      expect(passes).to.equal('validation skipped')
+    })
+
+    ///////////////////
+    // test suite 209 //
+    ///////////////////
+    it('should skip validation when field value is undefined', function * () {
+      const data = { username: undefined }
+      const field = 'username'
+      const message = 'Username should be a string'
+      const get = _.get
+      const args = []
+      const passes = yield Validations.string(data, field, message, args, get)
+      expect(passes).to.equal('validation skipped')
+    })
+  })
+
 })