Add themeRequestError reducer and getThemeRequestError selector and tests.

client/state/themes/reducer.js

@@ -2,7 +2,7 @@
  * External dependencies
  */
 import { combineReducers } from 'redux';
-import { mapValues } from 'lodash';
+import { mapValues, omit } from 'lodash';
 
 /**
  * Internal dependencies
@@ -161,6 +161,29 @@ export function themeRequests( state = {}, action ) {
 	return state;
 }
 
+/**
+ * Returns the updated site theme requests error state after an action has been
+ * dispatched. The state reflects a mapping of site ID, theme ID pairing to a
+ * object describing request error. If there is no error null is storred.
+ *
+ * @param  {Object} state  Current state
+ * @param  {Object} action Action payload
+ * @return {Object}        Updated state
+ */
+export const themeRequestErrors = createReducer( {}, {
+	[ THEME_REQUEST_FAILURE ]: ( state, { siteId, themeId, error } ) => ( {
+		...state,
+		[ siteId ]: {
+			...state[ siteId ],
+			[ themeId ]: error
+		}
+	} ),
+	[ THEME_REQUEST_SUCCESS ]: ( state, { siteId, themeId } ) => ( {
+		...state,
+		[ siteId ]: omit( state[ siteId ], themeId ),
+	} )
+} );
+
 /**
  * Returns the updated theme query requesting state after an action has been
  * dispatched. The state reflects a mapping of serialized query to whether a
@@ -267,6 +290,7 @@ export default combineReducers( {
 	// queryRequests,
 	// lastQuery
 	themeRequests,
+	// themeRequestErrors
 	activeThemes,
 	activeThemeRequests,
 	activationRequests,

client/state/themes/selectors.js

@@ -59,6 +59,18 @@ export const getTheme = createSelector(
 	( state ) => state.themes.queries
 );
 
+/**
+ * Returns theme request error object
+ *
+ * @param  {Object}  state   Global state tree
+ * @param  {String}  themeId Theme ID
+ * @param  {Number}  siteId  Site ID
+ * @return {Object}          error object if present or null otherwise
+ */
+export function getThemeRequestErrors( state, themeId, siteId ) {
+	return get( state.themes.themeRequestErrors, [ siteId, themeId ], null );
+}
+
 /**
  * Returns an array of normalized themes for the themes query, or null if no
  * themes have been received.

client/state/themes/test/reducer.js

@@ -30,6 +30,7 @@ import reducer, {
 	queries,
 	lastQuery,
 	themeRequests,
+	themeRequestErrors,
 	activeThemes,
 	activationRequests,
 	activeThemeRequests,
@@ -464,6 +465,103 @@ describe( 'reducer', () => {
 		} );
 	} );
 
+	describe( '#themeRequestErrors()', () => {
+		it( 'should default to an empty object', () => {
+			const state = themeRequestErrors( undefined, {} );
+
+			expect( state ).to.deep.equal( {} );
+		} );
+
+		it( 'should create empyt mapping on success if previous state was empty', () => {
+			const state = themeRequestErrors( deepFreeze( {} ), {
+				type: THEME_REQUEST_SUCCESS,
+				siteId: 2916284,
+				themeId: 'twentysixteen'
+			} );
+
+			expect( state ).to.deep.equal( {
+				2916284: {}
+			} );
+		} );
+
+		it( 'should map site ID, theme ID to error if request finishes with failure', () => {
+			const state = themeRequestErrors( deepFreeze( {} ), {
+				type: THEME_REQUEST_FAILURE,
+				siteId: 2916284,
+				themeId: 'vivaro',
+				error: 'Request error'
+			} );
+
+			expect( state ).to.deep.equal( {
+				2916284: {
+					vivaro: 'Request error'
+				}
+			} );
+		} );
+
+		it( 'should switch from error to no mapping after successful request after a failure', () => {
+			const state = themeRequestErrors( deepFreeze( {
+				2916284: {
+					pinboard: {
+						error: 'Request Error'
+					}
+				}
+			} ), {
+				type: THEME_REQUEST_SUCCESS,
+				siteId: 2916284,
+				themeId: 'pinboard'
+			} );
+
+			expect( state ).to.deep.equal( {
+				2916284: {}
+			} );
+		} );
+
+		it( 'should accumulate mappings', () => {
+			const state = themeRequestErrors( deepFreeze( {
+				2916284: {
+					twentysixteennnnn: 'No such theme!'
+				}
+			} ), {
+				type: THEME_REQUEST_FAILURE,
+				siteId: 2916284,
+				themeId: 'twentysixteen',
+				error: 'System error'
+			} );
+
+			expect( state ).to.deep.equal( {
+				2916284: {
+					twentysixteennnnn: 'No such theme!',
+					twentysixteen: 'System error'
+				}
+			} );
+		} );
+
+		it( 'never persists state', () => {
+			const state = themeRequestErrors( deepFreeze( {
+				2916284: {
+					twentysixteen: null
+				}
+			} ), {
+				type: SERIALIZE
+			} );
+
+			expect( state ).to.deep.equal( {} );
+		} );
+
+		it( 'never loads persisted state', () => {
+			const state = themeRequestErrors( deepFreeze( {
+				2916284: {
+					twentysixteen: null
+				}
+			} ), {
+				type: DESERIALIZE
+			} );
+
+			expect( state ).to.deep.equal( {} );
+		} );
+	} );
+
 	describe( '#activeThemes()', () => {
 		it( 'should default to an empty object', () => {
 			const state = activeThemes( undefined, {} );

client/state/themes/test/selectors.js

@@ -10,6 +10,7 @@ import { values } from 'lodash';
 import {
 	getThemes,
 	getTheme,
+	getThemeRequestErrors,
 	isRequestingTheme,
 	getThemesForQuery,
 	getLastThemeQuery,
@@ -130,6 +131,32 @@ describe( 'themes selectors', () => {
 		} );
 	} );
 
+	describe( '#getThemesRequestError()', () => {
+		it( 'should return null if thre is not request error storred for that theme on site', () => {
+			const error = getThemeRequestErrors( {
+				themes: {
+					themeRequestErrors: {}
+				}
+			}, 'twentysixteen', 413 );
+
+			expect( error ).to.be.null;
+		} );
+
+		it( 'should return the error object for the site ID, theme ID pair', () => {
+			const error = getThemeRequestErrors( {
+				themes: {
+					themeRequestErrors: {
+						2916284: {
+							twentysixteen: 'Request error'
+						}
+					}
+				}
+			}, 'twentysixteen', 2916284, );
+
+			expect( error ).to.equal( 'Request error' );
+		} );
+	} );
+
 	describe( '#isRequestingTheme()', () => {
 		it( 'should return false if there are no active requests for site', () => {
 			const isRequesting = isRequestingTheme( {