lib/rules/operator-whitespace.js
function inspectVariableDeclaration(emitted) {
            let node = emitted.node, code = sourceCode.getText(node);

            if (emitted.exit) {
                return;
            }

            //if a particular character is '=', check its left and right for single space
            for (let i = 2; i < code.length; i++) {
                if (code [i] === "=") {
                    (!/^[^\/\s] $/.test(code.slice(i-2, i))) && context.report({
                        node: node,
                        message: "There should be only a single space between assignment operator '=' and its left side." 
                    });

                    (!/^ [^\/\s]$/.test(code.slice(i+1, i+3))) && context.report({
                        node: node,
                        message: "There should be only a single space between assignment operator '=' and its right side." 
                    });
                }
            }
        }
function inspectVariableDeclaration(emitted) {
            let node = emitted.node, code = sourceCode.getText(node);

            if (emitted.exit) {
                return;
            }

            //if a particular character is '=', check its left and right for single space
            for (let i = 2; i < code.length; i++) {
                if (code [i] === "=") {
                    (!/^[^\/\s] $/.test(code.slice(i-2, i))) && context.report({
                        node: node,
                        message: "There should be only a single space between assignment operator '=' and its left side." 
                    });

                    (!/^ [^\/\s]$/.test(code.slice(i+1, i+3))) && context.report({
                        node: node,
                        message: "There should be only a single space between assignment operator '=' and its right side." 
                    });
                }
            }
        }
statement like `var x = 10` doesn't come under AssignmentExpression, so needs to be checked separately